What are the numbers with a six speed manual with 3.42 gears compare with six speed autos with 3.73? And what are the RPMs at 55-70ish? Thanks

 

I have 325/70R17 tires and a GPS-verified calibrated speedometer so my figures will be slightly off from a stock truck with stock error in the speedometer.

At 63mph I am at 1600rpm. At 70mph i am at 1750rpm.

 

Here are the numbers from the time I bought my truck a few months ago. Mine is an '08 3500 SLT 4x4 (non dually).

The low numbers are when I'm hauling a 33' Toy Hauler or one of my other trailers. Most of my driving is a combination of Highway/Town. The DIC computer tends to be about 10% optimistic as you can see.

At this time my truck is as stock as I bought it. My previous truck was an '01 Duramax w/Allison transmission. Currently, I doubt that I'm driving the 6 speed manual efficiently enough to optimize fuel mileage.

 

I get 17-17.5 on a typical tank of fuel. I drive 20-30 miles on the highway and a little stop and go. Long trips on the highway I have gotten up around 19-19.5 running 70-75mph.

I am running 75 psi in the tires, which makes it ride rougher. All of these are from the OH display. I have found it to be pretty accurate, but sometimes .5-1 mpg off

I drive it easy most of the time, but every once in a while I blow the soot out.

 

My truck started life at 17 to 18 MPG. After Deletes I am now showing 20 to 20.5