Yeah, and used prices in that range are usually like $5000+ cost adder for the cummins. That plus the fact that Diesel is ~10% more than gas at the pump, you are never making up the price difference with fuel economy.
For what you do, Beef, I think the V8s will be just fine.
I know from a braking/stability/comfort standpoint, I could go 80mph and not even feel the trailer with that setup. Very comfortable, drove well.