There is so much misinformation on this thread. It's too much effort to respond to all of it but on the other hand, I don't think you need a diesel, so I don't think it matters. This is not the site to get reliable diesel information.
If you only drive 3000 miles a year and mostly on level ground, I don't think you'll ever come out on a diesel. Instead, look for a gas engine with the proper gearing for the engine size. Most DRWs will probably have 4.10s or similar and will be fine. Sure a diesel will work, but most don't like being barely used and that goes for the 6.0 in particular.
An alternative is to change the gearing on the current truck you have with some minor upgrades such as exhaust and higher flowing air filter if you haven't done that. Of course, it won't carry a TC as well as a DRW, so in that respect, you'd be better off doing the same type modifications to a DRW.