I'm biased, but it sounds like you need a Cummins
I'll freely admit that I don't actually need as much truck as I have, but it looks to me like it might be just what you need. You can get a good deal on one 4-5 years old that you'll still get a ton of life out of. Average time to first overhaul is about 350,00 miles. I bought my 2007 w/ 70,000 on it for about $17k (about 1/2 the price of new). A pre-DPF truck (before 2007.5 w/ the 6.7L engine) should give you mpgs in the low 20's stock (unloaded). I think the better FE and longer life should pay you back for the extra cost of the diesel.