A 12 year old truck, particularly a diesel, is far from being worn out. You must have an '06 Duramax? That is a very sought after, valuable truck. Most people that own one of those wouldn't get rid of it for any reason. Lots of power, 6 speed Allison, no emissions, basically no chronic problems of any kind.
My own Chevy is an '05 with 227,000 miles on it. I wouldn't hesitate to drive it anywhere.
If you really want gas I'd look at the RAM 6.4 Hemi. Not that the GM 6.0 is bad but the 6.4 makes more power and, having driven both, it feels like it has more power, probably due to GM's excessive torque management software.
I'm just not a fan of Fords, everyone I've ever been associated with has been full of problems, most of them very expensive.