Duramax vs Power Stroke Fuel Economy Tow Test and Drag Race

ShinerBock wrote:

Cummins12V98 wrote:
"I think the 3.42 rear end on the GM might have had an effect on mpg here especially if they let the truck do all the shifting."

But But, I thought the magical 10 speed was supposed to keep the engine in the perfect rpm???

This is not due to it being a 10-speed but rather the trans tuning. Shifting manually or having a shorter final gear would alleviate this. To be fair, I had to do the same in my 68RFE when it had stock trans tuning and so do my friends and family who have Aisin's so Ram's stock trans tuning is not perfect either.

When do you manually shift a transmission with stock tuning? What are you trying to accomplish by manually shifting?