I'd vote on the Dodge Cummins, 5.9 with MANUAL trans. Uses the least fuel of all your choices. Super easy to do maintenance, Just pop the hood of a Chevy or Ford a mechanics worst nightmare (BTW, I am an exe prof. mechanic). Then look at the Cummins. It is clean and simple. I was always a Toyota/Nissan/Isuzu kinda' guy. I then bought a 2003 Ford F250, manual, gas truck. Piece of junk. Full of defects right from the factory. Best tanks were 12 mpg. In 2006 I got a new Diesel Dodge manual. Zero defects. Now, 3 years later and thousands of miles of very rough off road work, it still has not required a single repair. Surprisingly the Dodge, at least my Dodge, has been much more reliable than any Toyota, Honda or Nissan that I have ever owned. Recently on a White Rim Trail trip I fueled up in Moab. My friend with a 2006 Toyota Tacoma 4cyl fueled up as well. At the end of the trip, the Toyota used 10 gallons. This Toyota required low gears on all the hills plus a lot of clutch slipping. My Dodge Cummins just idled over every obstacle in high gears. My fuel consumption for the very same White Rim Trail trip? 8 gallons. Fully 20% more efficient than the little cramped Tacoma! Plus I had the luxury of 75:1 crawl ratio, high ground clearance and full suspension travel.
I can't recommend highly enough the manual trans. Besides better economy, you get much greater reliability and simplicity. An automatic can instantly fail completely, a manual will give you thousands of miles of warning. If you watch the following video clip, you'll see Jay's automatic Dodge making all sorts of noise, his RPM's very high, torque converter slipping like crazy, coming up the steep hill. Jay's truck throws all the rocks out that were carefully placed. My manual simply idles up, very low rpm even though the obstruction is now more severe.
Whatever truck, get a manual. Click here:
Oh yeah, one more thing, you don't need no stinkin' electric sway bar disconnects. Just remove the sway bars completely!