Personally, I've found the smaller trucks really don't do any better on fuel than a full size so you might as well have a full size truck. In fact, I got rid of a Nissan Frontier because I figured if I was only going to get about 16 mpg I might as well have something a little roomier.
I get up into the mountains a few times a year pulling a small trailer and every time I do I wish I had a diesel. The rest of the time a gas engine suits me just fine.
My daily driver is a 2008 Chevy 3/4 ton with a 6.0 gas engine. Even loaded to almost full GVW the thing has plenty of power. Of course it only gets about 13 mpg on the highway. But keep in mind mine weighs in right at 9000 pounds and I don't pay for gas so I'm a bit heavy on the throttle all the time.