OK, I have been monitoring a lot of threads here regarding MPG and such with the Duramax. Yes I finally understand less than 2000 RPM will result in great but not necessarily exceptional milage.

A buddy of mine just got a Dodge 2500 Diesel for his work which invlolves towing a 34' trailer. He has the manual transmition in the truck and I have not really been able to get any MPG info from him but he was talking about lugging the combination in 4th gear (it is a six speed) from 40 MPH or so and having really good response.

I don't really have any problem believing that.

But it got me kind of got me curious about what effect the manual transmition could have on keeping the RPMs in the under 2000 RPM zone and MPG. Being relatively new to the Duramax and having desired an automatic transmission any way, I just wonder if there might be something to having a manual trans that might keep the engine in the "lug" mode where torque is maximum and efficiency is best that maybe I don't have with the Allison?

Thanks!

If you are a very skillful driver, who always shifts at the right time, I'm sure you can get 10-15% better mileage with a standard.

This is based mostly on my own experience with a 93 K2500 6.5 standard.

However, most people won't mange their shifts well enough to achieve that.

A good driver with an Allison can probably beat the mileage achieved by a poor driver with a standard.

Last month (Nov 15 - 30) I completed a trip from So. California to N. Arkansas. Here are my mileage results:

Eastbound Route: 1691 miles, I-15 to I-40 to I-44 to US-412.
For the most part, cruise control was set on 75 mph and overall mileage was 17.2 mpg.
Westbound Route: 1901 miles, Hwy 5 to I-30 to I-20 to I-10.

Cruise set on 75 mph, except for about 200 miles at 50mph due to snow/ice in central Texas. Overall mileage was 17.6.
Tuning was stock. No significant load in vehicle. No towing. Cab high shell on bed. Tires are 285-75-16 on PYO wheels. Speedo corrected to GPS. Running Stanadyne PF in fuel. Temps were on the cool (40 to 60) side going Eastbound. Temps Cold (15 to 40) on the Westbound leg. No winter front.

When driving my 3500 Dually CC 4X4 in just everyday situations, some city, some rural, no interstate, I get around 19.5 MPG. I don't know what it will get on the interstate as when I'm on the interstate I'm usually pulling my 33' fiver which weighs in at around 13K. With it, I get about 15 MPG on the interstate. I have the 6-speed. Hope this helps. Oh, and by the way, no overheating.

Last month (Nov 15 - 30) I completed a trip from So. California to N. Arkansas. Here are my mileage results:



Eastbound Route: 1691 miles, I-15 to I-40 to I-44 to US-412.For the most part, cruise control was set on 75 mph and overall mileage was 17.2 mpg.
Westbound Route: 1901 miles, Hwy 5 to I-30 to I-20 to I-10.

Cruise set on 75 mph, except for about 200 miles at 50mph due to snow/ice in central Texas. Overall mileage was 17.6.
Tuning was stock. No significant load in vehicle. No towing. Cab high shell on bed. Tires are 285-75-16 on PYO wheels. Speedo corrected to GPS. Running Stanadyne PF in fuel. Temps were on the cool (40 to 60) side going Eastbound. Temps Cold (15 to 40) on the Westbound leg. No winter front.


This is pretty close to what I usually get.

When driving my 3500 Dually CC 4X4 in just everyday situations, some city, some rural, no interstate, I get around 19.5 MPG. I don't know what it will get on the interstate as when I'm on the interstate I'm usually pulling my 33' fiver which weighs in at around 13K. With it, I get about 15 MPG on the interstate. I have the 6-speed. Hope this helps. Oh, and by the way, no overheating.

I can get what you get empty if I really baby the truck and keep it at or under 65. Actually, Ive gotten as high as 22. No way I get that much towing my 12K 5er. Closer to 10.5. I have the 5 speed and no overheating issues (yet).

When driving my 3500 Dually CC 4X4 in just everyday situations, some city, some rural, no interstate, I get around 19.5 MPG. I don't know what it will get on the interstate as when I'm on the interstate I'm usually pulling my 33' fiver which weighs in at around 13K. With it, I get about 15 MPG on the interstate. I have the 6-speed. Hope this helps. Oh, and by the way, no overheating.

That's pretty good mileage! Especially pulling a 13K fiver. BTW, what rpm's are you indicating (on level ground) at 70mph in 6th gear? On my 5-speed Allison I'm indicated 1950 rpm's at 70. RPM's would be about 2250 at 70 if I were running the stock tires, but my tires are 285-75-16.

manual is always better