I'm not familiar with Dodge or Chevy in those years but have seen lots of positives posts about Cummins and Duramax diesel motors. Ford definitely had problems with the 6.0 motors, but those can be resolved at a hefty price. On the other hand, there are obviously lots of 6.0 motors out there with no issues. I took a chance buying my signature TV but a couple of the mods had been done and I rationalized that at 146,000 miles when I bought it, it would be okay. Time will tell. Bottom line is you takes yer chances when you buy any used vehicle, and diesel motors do cost more to maintain. If you can find a Chevy with the big 8.xx motor or the Ford with a V10 (hard to find), that might be a good route to take. If you wait a year or two you may be able to find a post 2007 Ford with the better motor in your price range.