Ive owned a Chevy with the 8.1 gas, and now have had 2 chevys with the duramax, all with the allison tranny. I miss my 8.1 because i had a nice exhaust on it, and it was my first nice truck, but when i go to the gas station i love my diesel. I got about 12-14 mpg with the 8.1, and it didnt really matter if i was hauling or not, my diesels i get about 16-19 and if im on the highway not hauling i can get just about 20mpg. Yeah the diesel cost a little more in the beginning (i paid 35000 for my truck, a 2008 crew cab), BUT with the duramax and allison it will last forever. We have a local livestock hauler who has one with 325000 mi on it and all he has replaced was an oil pump.