[mudman]

Seems like most comments address power plant choices, I think the trans is just as big of a factor in your case. I love the Allison 1000 in GM trucks.

Just for additional data: I had a 2500HD 8' bed extended cab 4x4 with a Vortec 8.1 gas tied to the allison 1000. 14mpg empty and cruise control at 65mph, 12mpg overloaded/towing or driving like a maniac.

Don't forget not all 3/4 ton and 1ton trucks are created equal, even from the same product line, ie bigger brakes, hd trans cooler, suspension etc differ depending on the package or options for that truck. IMO these items are very important to consider in your situation both for longevity of the equipment, safety and comfort.