My 97 Suburban does ok, but I am getting 14.5+ with 4:10 gears and the upgrades listed in my signature below. But folks tell me my injectors are the original ones, so I need to change them and the exhaust, then I should peak out at 18 to 19 mpg???
* But I hear if I change gears from 4:10 to 3:73 or 3:42, I should be 22mpg?
* I use AmsOil diesel oil & AmsOil fuel treatment.
Help, fuel prices are soaking us dry...

In my 95 crew cab listed in sig, I have gotten as high as 20mpg, average 16 mixed driving and 17 towing a 20ft gooseneck with 5 Polaris ATV's, roughly 8000lbs trailer total trailer weight. Its a Manual, not sure if that helps or not, know it does on some cars. It also has 4.10 gears.

Gearing, gearing, gearing, and then there is "how heavy is your foot"? The best I have seen on my truck has been around 22mpg @60mph average. Probably would do a bit better if I cruised at 55 but then I get enough looks on the interstate already. Towing a 7500 lb. 5th wheel then it drops to 10-13 depending on terrain.

3.73s will get you better mileage than 4.10s. the engine spins slower with the 3.73s. my truck has 3.73s and i'm at roughly 2,000 RPM at 60-ish MPH. i've gotten in the high 20s while on the highway crossing the state. i think it worked out to about 24 MPG roughly. but that was with no load other than the truck itself and me and my dad in the cab. i've heard that its harder to tow with 3.42's and that 3.73s tow better and the 4.10s tow better than the 3.73s. this is just what i've heard though.

My 95 with 3:73's got 18 when it was new up until just recently when I opened up the S intake and blocked off the EGR and it jumped up to 20. Then winter diesel showed up and i'm squeezing 17 out of it now. From what I've read on here if you get 22 with 4:10's you are part of the crowd on this board that are really living right.

it sounds like you are ready to buy tires. i would by bigger tires final gear ratio between 3.73 and 4.10 is only 2inchs

3.73 with 31" tires will be the same as 4.10 with 33" tires final gear

Wow, what is the S intake?
How does one block the EGR?
Educate me, if the EGR is blocked, does that damage anything? Now with my Heath Diesel computer that already has all the programming changed and I assume EGR feedback and function, maybe the EGR change for this would not really do anything, not sure?
Thanks for all the replies :)

My 95 with 3:73's got 18 when it was new up until just recently when I opened up the S intake and blocked off the EGR and it jumped up to 20. Then winter diesel showed up and i'm squeezing 17 out of it now. From what I've read on here if you get 22 with 4:10's you are part of the crowd on this board that are really living right.

it sounds like you are ready to buy tires. i would by bigger tires final gear ratio between 3.73 and 4.10 is only 2inchs

3.73 with 31" tires will be the same as 4.10 with 33" tires final gear
Oh, this is nice insight!!!! Thanks.
Is there a chart posted somewhere on tire sizes and changing ratio's?
Then if I change my tire size, does that mean I need to have Heath adjust the computer I bought from them, because when I bought the computer, they needed to know the VIN which gave the 4:10 ratio??

Need to verify your engine is an S code, do you know for sure it has an EGR? If it does it's an S code, if it doesn't you already have an F intake and there is no improvement to be done to the intake.

I'm toying with the idea of putting a Gear Vendors overdrive on mine. They're really spendy though. You can buy a lot of fuel for what one of those things costs (about $2200 I think). I have to have the 4.11's cuz I tow.

Things could be worse. My 1991 gasser Suburban V2500 with a 5.7, 4.11, and a 4L80E gets just over 11 mpg. Best I ever got was almost 14. ...and that thing is a dog! It can hardly get out of its own way. It is, however, very dependable. I'm thinking I'd better keep it as a backup to the K3500 in my sig.

Need to verify your engine is an S code, do you know for sure it has an EGR? If it does it's an S code, if it doesn't you already have an F intake and there is no improvement to be done to the intake.

My VIN # has a F in it, is that what you are reffering to for F vs S code?
10th letter from the right is an F (8th letter from the left) ?
VIN# 1GKGK26F4VJ712694

Oh, this is nice insight!!!! Thanks.
Is there a chart posted somewhere on tire sizes and changing ratio's?
Then if I change my tire size, does that mean I need to have Heath adjust the computer I bought from them, because when I bought the computer, they needed to know the VIN which gave the 4:10 ratio??

google "tire size calculator" all types of calc's pop up. Ed

Speedometer is corrected by modifying or replacing the DRAC, digital ratio axle controller .

Yes, you have the L65, "F" engine. Also, 4.10's are preferred for towing, makes it much easier on the engine to tow large loads. The truck in my sig got roughly 14 MPG as it sits over this past summer. I hope to see a little closer to 16 with the exhaust. I have 3.73's, as do many C/K1500's with the 6.5.

Just so I know, hos did you translate the VIN # to id I have a L65 & F?
What does the L65 stand for?

L65 is the RPO code in your glovebox for the engine, like the DMAX has LB7, LLY, LBZ, and LMM. F is the 8th letter of your vin, also a code for the engine. IIRC, there are three 6.5's, the light duty turbo, L56, VIN S, heavy duty turbo, L65, VIN F, and N/A, L57, VIN P. I know I have the L56 and L65 right, but I'm not 100% positive on the L57, as that's just what I've gathered on various sites.

I have 4.10 gears in mine and I am getting about 13.5mpg on B-99 biodiesel. On straight petroleum diesel I usually get around 15. I am still playing around trying to tweek my wastegate settings, so things might improve when I find the sweet spot and stop putting my foot in it so much. Tire wise I am running the 265/70/16's ( at least I think they are 70 profiles, might be 75's though. The alternative standard size)

I am getting 19 mpg on the highway at 70 towing a 18ft car trailer loaded. the truck has 151k and 4:10 gears and a health diesel exhaust

I get 20 on the interstate on winter fuel with my truck with 4.10's. Any over 70mph tho and the mileage drops fast!!!

I put a slightly taller skinnier tire on. (32.5x8.5 i believe) but what is your tachometer at when you are doing 70mph? With 4:10's?

L65 is the RPO code in your glovebox for the engine, like the DMAX has LB7, LLY, LBZ, and LMM. F is the 8th letter of your vin, also a code for the engine. IIRC, there are three 6.5's, the light duty turbo, L56, VIN S, heavy duty turbo, L65, VIN F, and N/A, L57, VIN P. I know I have the L56 and L65 right, but I'm not 100% positive on the L57, as that's just what I've gathered on various sites.

All info looks right to me, only I have no clue about the L57, P VIN is right though.

Think of "S" in the VIN # as LD (light duty) and "F" as HD.
S (or L56) engines had EGR to help with emissions because it was a diesel engine used for personal transportation to appeal to the masses and an upper intake that is one giant restriction, doesn't make as much power from the factory. Also from owning a 95 previous to truck in sig, when exiting the highway, tryin to goose it over the hill, it just felt really bogged down, because of the HOT Exhaust being dumped into the intake.

F (L65) lacks said above, and makes more power from the factory. She also boogies up that hill a LOT faster then the other one ever could even with the EGR blocked off.

I'm clocking consistent 15.4 mpg in mixed driving-not pulling the horse trailer.
This tank I'll change to the new 190 thermostat to see if that helps, currently running a 170.
These numbers are after installing a 4" exhaust and testing it without the soot trap.
I've still got the original injectors at 230k as well.
Mike