Well two things. One you have run a diesel about 250k to break even in savings vs gas. Second is unless your doing a big fifth wheel then a heavy duty 3/4 set to tow will do you fine. Chev, Ford, and Dodge all have packages.

Many get the Duramax with the Allison to pull a fifth and Fords has come around compared to what they were a few years back. Dodge has a truck that is set and made to pull a heavy trailer. If you have the money and don't mind parting with it you will love a decked out diesel. Gas will do you fine also and cost you much less. Either way a bunch of $$$$$ are leaving you just have to pick how many.