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The tachometer is one of the options in the small driver info display where you toggle through things like the trip meter, mpg, and outside temp. It's annoying how the tach only counts in 100 rpm increments. That's why I said 1900-2000 rpm. It switches between those values right around the 75mph mark.
 

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The tachometer is one of the options in the small driver info display where you toggle through things like the trip meter, mpg, and outside temp. It's annoying how the tach only counts in 100 rpm increments. That's why I said 1900-2000 rpm. It switches between those values right around the 75mph mark.
and this feature is only on 2008+ vans i'm guessing.
personally i use my bully dog tuner to give me rpms. a scangauge will work also.
 

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Yeah I use my Banks IQ to read my RPM's since my/our earlier model vans didn't come with them. I didn't know that the 2008+ Vans had some kind of tachometer, even if it is in the info center.
 

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Is gearing the van up to run lower RPM at cruising speeds really a viable option to increase fuel mileage? How much fuel consumption is related to RPM vs. aerodynamics? I forgot to check what RPM my wife's LML truck runs at 75 MPH.
 

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It's a pretty big difference actually. That's why auto manufacturers keep coming out with transmissions that have more and more gears. GM is supposed to come out with a 10 speed transmission within the next few years for that exact reason, trying to get the RPM's in the lower more ideal lower operating range when cruising. I think it's a bit overkill but to deal with the CAFE requirements auto manufacturers are increasing the complexity of the drivetrain and engine efficiencies.
 

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If Allison can make it work you will see a CVT, constant variable transmission, in the future. They announced they were working on one last year so I would assume it will be out in a few years.
 

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I hope I am out of fixing cars in the next 5 years, they are simply getting ridiculously complex for minute gains, :(

Is gearing the van up to run lower RPM at cruising speeds really a viable option to increase fuel mileage? How much fuel consumption is related to RPM vs. aerodynamics? I forgot to check what RPM my wife's LML truck runs at 75 MPH.
I don't own one but I can't see how 2-300 rpm decrease will do anything. In my personal experience, that kind of rpm difference hasn't done anything for me in a lot of vehicles over the years I've played with. I would say the magic number to that would make a difference is 500+ rpm.
 

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If Allison can make it work you will see a CVT, constant variable transmission, in the future. They announced they were working on one last year so I would assume it will be out in a few years.
God I would hope not!!! I can't stand CVT transmissions! They drive me absolutely NUTS!!!
 

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I hope I am out of fixing cars in the next 5 years, they are simply getting ridiculously complex for minute gains, :(



I don't own one but I can't see how 2-300 rpm decrease will do anything. In my personal experience, that kind of rpm difference hasn't done anything for me in a lot of vehicles over the years I've played with. I would say the magic number to that would make a difference is 500+ rpm.
1800 rpm range will yield better results than the 2200 rpm range at 72 us van guys are seeing with the 4L85e. 2000 rpm seems to be the turning point for us so a 200-300 rpm drop would be great.
 

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God I would hope not!!! I can't stand CVT transmissions! They drive me absolutely NUTS!!!
Ditto, I drive one and want to get out right away, :(

1800 rpm range will yield better results than the 2200 rpm range at 72 us van guys are seeing with the 4L85e. 2000 rpm seems to be the turning point for us so a 200-300 rpm drop would be great.
Interesting. How much MPG increase do you see? Is it worth the cost for the extra MPG?
 

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At 65mph on the highway, my pickup with the Allison only gets .5 mpg better than my much larger CargoMax van does with the 4L85E. On the highway, road speed is the big factor. At times, the pickup gets better mileage when I drop it into 5th...I believe dutchpilot ran his in 5th when he had trailers hooked on. Given the miles he runs, I imagine he had it figured out.

Getting up to speed, or in town...the extra gears will help with fuel mileage as you are doing more of the work mechanically rather than with the hydraulic slip of a torque converter. A 4 speed wastes a lot of engine power floating through 4 fairly tight gear ratios. If I spend all day in the city, my mileage in the van is terrible.
 

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I have seen some of my best MPG numbers in the Winter due to the fact I had to drive slower which puts me under 2,000 RPM.

If I was starting over again with my current van I would look at going with a Gear Vendor instead of the Allison. With me driving 40k-50k miles a year I could justify the cost with a 1 MPG or more increase in mileage.
 

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I have seen some of my best MPG numbers in the Winter due to the fact I had to drive slower which puts me under 2,000 RPM. .
Considering the bumper/guard you have on the front, and the laws of physics, I'd say at least 7/8 of your mileage improvement is from lower aerodynamic drag. Staying under 2000rpm means you are slowing down quite a bit from your normal 72mph. Aero drag is exponential.
 

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At one point I also was interested in an Allison swap. Now I wouldn't even consider it. But then I already have a 6L90, so that makes the decision a lot easier than if I had the 4-speed. From what Ben Tyler has said, the 6L90 swap is fairly easy on a 2008-2009 DMax van, because it has the newer GMT900-style electronics required to control it.

In addition to being a lot heavier, the Allison also has much higher parasitic losses than a 6L90 (i.e.: it takes more power to drive the Allison than a 6L90). In most cases this will more than offset minor differences in overall gearing. The 6L90 also has a wider overall gear ratio range than the Allison, including a "stump-puller" 4.03 first gear (compared to the Allison's 3.10 first gear). If towing a heavy load from a standstill, that lower first gear is definitely an advantage, especially since a van will probably be limited to lower maximum torque than a pickup (smaller cooling system, etc., although the cooling limitation imposes a limit on power output, not torque). Another way to look at this is that 6L90 which is inherently weaker than an Allison, makes up for that somewhat by having more torque multiplication in first gear.

Of course, theoretically, on the other end of the speed range, you are better off with a lower top gear ratio and a higher axle ratio (Pickups have a 5% shorter axle ratio and the Allison has a 9% taller top gear) because a higher rear axle ratio gives the transmission more leverage against the rear tires (tire diameter also affects this for the same reason). But the overall strength also depends on exactly how the transmission manages to accomplish that "tall" overdrive final gearing.

I contacted this company (which is the only one I've found that advertises performance 6L90 rebuilds, though surely there must be many others who might be able to do it), and was told that their built 6L90 will work fine behind a Duramax with quite a bit more torque than a pickup truck LMM. If you read the specs of what they do, notice that they replace the stock intermediate shaft with a billet part. So apparently there is a lot of room for improvement over the oem tranny by using upgraded materials. I guess that an upgraded 6L90 running higher hydraulic pressure might have slightly higher parasitic losses than a stock 6L90, but it's *probably* still a lot less than an Allison. Here's the info from their website:

Super 6L90 Transmission build
Send us your 6L90 transmission and we'll transform it to the most reliable unit there is anywhere!
Complete rebuild with all new gaskets, seals, rings & filter. New pistons & retainers where needed.
Alto PowerPacks® in the 4/5/6 , 3/5/Rev & 2-6 clutch packs, this transmission's weakest links. Alto's state of the art Red Eagle® friction material incorporated with additional plates added to the clutch packs for a major increase in capacity!
Raybestos or B&W h/d frictions in the low/rev clutch pack & 1/2/3/4 pack.
300m Billet Intermediate Shaft (output carrier shaft-4/5/6 hub) with improved thrust bearing. Now that we've got the clutch packs holding better, the OEM powedered-metal shaft is twisting & breaking with increased H.P., the next weak link.
4-5-6 "Powerglide Powerpack" hub & clutch kit. Our latest improvment. This kit allows us to use the Red Eagle Powerglide frictions that are twice as wide as the conventional 4-5-6 friction for double the surface area and twice the holding power! This kit incorporates custom made pressure plates for the P.G. clutch that also resist coneing & warping. This also allows us to run much higher 3-4 shift pressures in the TCM tune than we could with the conventional PowerPack for even more wot shift consistancy & reliability.
Century reinforced clutch hubs for increased reliability.
Wide inlet filter
Century's proprietary valve body ugrades.
Performance Transmission Tune Included! A proper performance TCM tune is very important for warranty, optimum transmission performance & longevity! We tune with HP Tuners software.
1 year warranty.
'08 and older units may require some internal factory updates at additional cost. We will advise you of updates, if needed after tear-down & inspection of your transmission.
Contact us for shipping arrangements & freight costs.
Price: $3,799.54
 

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These guys also have a 6L80/90 improvement program. Sounds like they have/use similar hardware...

I called them and they thought that a 6L90 would be able to live behind LML power (350HP/750ft-lbf) with just their 4 disc torque converter and software to optimize shift timing/pressures. Don't go attaching a 15k trailer and expect it to live (per their recommendation), but should move the van around just fine.

If you really want to kick up the power/torque or (not and) pull a heavier trailer, etc, then you can go into the internals and add clutches and such. It'll never hold what an Allison will, but if you want that, just swap the Allison in.

I'm in no way affiliated with them - just presenting another option
 

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Would the 6L90E swap be a more challenging swap to do that an Allison in regards to TCU integration? I'd like to swap in a 6 speed transmission when I do my 4x4 swap, Allison is a challenge but hoping the 6L90E would be easier. I have a 2006 model.
 

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Would the 6L90E swap be a more challenging swap to do that an Allison in regards to TCU integration? I'd like to swap in a 6 speed transmission when I do my 4x4 swap, Allison is a challenge but hoping the 6L90E would be easier. I have a 2006 model.
My guess would be that with a 2006 van that has the GMT800-style electronics, physical fit issues aside, an Allison would have to be a lot easier because you could use 2006 DMax pickup truck electronics. GMT900-style electronics use a completely different (faster) communication protocol that I would assume would be difficult to integrate. Not saying somebody couldn't improvise a solution, but I don't think it would be as easy as being able to use all oem components.

Not surprisingly, GM vans have a lot in common with their pickup truck counterparts. Pickup trucks are upgraded first; vans are always a year or two behind, but once the vans 'catch up' to the pickups, they are the same again.

This is the problem with any pre-2008 LMM van, which would have a GMT900-style DMax in a vehicle with the older GMT800-style electronics, which would really make it an oddball. Although, I'm not sure how many of those were actually built? In the past, GM has just stopped offering DMax vans until the electronics, etc. are updated.
 

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FWIW (from GM powertrain):

6L90 vs. 6L80

The 6L90 is a heavy-duty version of the 6L80 six-speed automatic, with a strengthened input gearset that has two additional pinion gears (six in total) and a strengthened output gearset that uses wider gears than the 6L80. Its flexibility extends to the clutches, where the 6L90 has one more clutch plate in each clutch than the 6L80 for heavy-duty applications. There is also a 6L90 version without the additional clutch plate to more closely match application requirements, where appropriate.

The 6L90 shares about 75 percent of the parts as the 6L80, although the case of the 6L90 is 35 mm longer than the 6L80 case. The 6L90's case also accommodates additional fasteners between the transmission and the transfer case for improved driveline noise/vibration performance.

6L90 is a six speed RWD / AWD, electronically controlled automatic overdrive transmission with torque converter clutch. Clutch-to-clutch architecture, with integral Electro / Hydraulic Controls Module
Maximum engine power: 452 bhp ( 337 kW ), Diesel: 300bhp ( 223kW ) - Truck
555 bhp ( 414 kW ) - Passenger car
Maximum engine torque: 531 lb-ft ( 720 Nm ), Diesel: 520 lb-ft ( 705 Nm ) - Truck
550 lb-ft ( 746 Nm ) - Passenger car
Maximum gearbox torque: 885 lb-ft ( 1200 Nm )
Gear ratios: MYD
First 4.030
Second 2.360
Third: 1.530
Fourth: 1.150
Fifth 0.850
Sixth 0.670
Reverse: 3.060
Maximum shift speed 6200 rpm
Maximum Validated Weights: ( Target ) GVW: 15,000 lb ( 6803 kg ), GCVW: 21,000 lb ( 9525 kg )
7-position quadrant: P, R, N, D, X, X, X ( X = available calibratable range position )
Case description: 3-piece ( Bell, main, extension )
Case material: die cast aluminum
Shift pattern: (2) Three-way on/off solenoids
Shift quality: Five variable bleed solenoid
Torque converter clutch: Variable Bleed Solenoid ECCC
Converter size: 300mm ( reference )
Fluid type: DEXRON® VI
Fluid capacity: w/ 300mm converter 300mm: 13.0L ( 10.8kg )
Transmission weight: w/ 300mm converter Wet: 109kg ( 240lb ) estimated
Pressure taps available: line pressure
Assembly Site:: GMPT Toledo, OH
GMPT Silao, MX
Available Control Features:: Multiple Shift Patterns ( Selectable )
Driver Shift Control ( Tap Up / Tap Down )
Enhanced Performance Algorithm Shifting ( PAS )
Selectable Tow / Haul Mode
Engine Torque Management On All Shifts
Altitude and Temperature Compensation
Adaptive Shift Time
Neutral Idle
Reverse Lockout
Automatic Grade Braking
Additional Features: OBDII / EOBD
Integral Electro/Hydraulic Controls Module ( Tehcm )
Control Interface Protocol - GMLAN
Applications: Chevrolet Suburban
GMC Yukon XL
Chevrolet Silverado HD
GMC Sierra HD
Cadillac CTS-V
Chevrolet Express
Chevrolet Camaro ZL1
GMC Savana

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Type: Six speed, rear-wheel-drive, electronically controlled, automatic, double overdrive transmission with torque converter clutch and park pawl
Engine range: 6.6L
Maximum Input Torque: 765 lb-ft
Maximum Input Power: 397 hp
Gear ratios: MW7
First 3.094
Second 1.809
Third: 1.406
Fourth: 1.000
Fifth 0.711
Sixth 0.614
Reverse: 4.480
Maximum shift speed 3300 rpm
Maximum validated gross vehicle weight: GVW
12,000 lb - 3600 series
11,400 lb - 3500 dually series
9,900 lb - 3500 non-dually series
9,200 lb - 2500 HD series
GCW
23,500 lb - 3500 dually, 3600 series
22,000 lb - 3500 non-dually
22,000 lb - 2500HD
6-position quadrant: P,R,N,D,M,1
Case material: die cast aluminum
Shift pattern: (3) on/off solenoids
Shift quality: Variable bleed solenoid control / adaptive shifts
Torque converter clutch: Variable Bleed Solenoid Control
Converter size: 310mm (diameter of torque converter turbine)
Fluid type: DEXRON® VI
Transmission weight: dry: 150 kg (330 lb)
Fluid capacity (approximate): shallow pan: 12L (13 qt.) (dry)
Power take off: provision available
Pressure taps available: main pressure
Assembly Site:: Baltimore, MD
Available Features:: Tapshift Range Selection Mode
Grade Braking
Cruise Grade Braking
Tow/Haul Mode
Shift Stabilization
Adaptive Shift Controls
Heater Performance Mode
Low Traction Mode
Exhaust Grade Braking
Exhaust Cruise Grade Braking
Applications: Chevrolet Silverado and GMC Sierra 2500HD, 3500


Although the above data is for the 2014 model year, it looks like they need to update the GCWR, etc. for the Allison.
 
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