Maybe look into adding a TransferFlow Aux tank to your Ram. We have a 96 gallon aux tank on our 2008 GMC 3500 Duramax and can go 1500 miles between fill ups. If you maintain your truck you shouldn't have to many issues. Over 132000 miles on our GMC with only the #8 glow plug having ann issue, took 30 minutes to replace.
If your hell bent on trading in, again, I'd put the money down on the new truck with your trade in and take the shortest loan possible. Keep the money now as it's probably making higher interest than your truck loan is.