Just remember that if you go with the Chevy or GMC with the Duramax?Allison setup that it has transimission assisted braking...in other words you don't need a 'Jake Brake'!
I get 10 t0 13MPG depending on speed!
2006 Flagstaff 831RLSS Travel Trailer
2007 Chevy 2500HD 'Classic' with the Duramax engine.
Converting a 1956 GMC PD4501 Scenicruiser, ex Greyhound into a motor home.