In the 3rd gen trucks both the mega cab short box and quad cab long box were built on a 160.5" wheelbase. 4th gen (2010 and up) mega cabs kept the 160.5" but the crew cab long boxes grew to 169.5" thanks to a bigger cab than the previous guad cabs. Either way they are big and clumsy till you get used to them. Having never driven a Duramax I can't comment on how they are for power, but moving from my '07 Ram to my '12 Ram was a big step up in power and the 68RFE is so much better than the old 48RFE trans. Still itching to tow with mine.