Those that drive a 10-13 speed transmission, or the auto shifts. Do Detroits get better mileage than cats, or cummings?

Actual MPG I get in my T2 is 6.8. Now when the company figures it they only count dipatched miles so they say I average 6.2 13 spd, cat acert.

My truck averages 6.8mpg. It's a '02 Volvo 770 with 805,000 miles, 10 speed autoshift. Our average hauls are 42,000lbs+ into and out of central West Virginia, so we see a *lot* of mountains.

When I take loads to El Paso, the fuel mileage jumps to about 7.5-7.8 after I get out of the hills.

Edit: Forgot the engine - Cummins 465hp ISX

I was born in Buckcannon and still try to get up their once a year. I would love to move back to WV one day, and always thought anyone who can drive a truck on those back mountain roads can drive one anywhere