Gary, while researching our change from gas to diesel we learned a few things about the 340hp vs 360hp or 380hp. Although our choice was not Tiffin, here are some things to look at:
I don't think you'll have much problem with hills no matter which diesel you choose.
The important thing to us ended up to be not how much we could 'tow' but how much can we safely 'carry' in the coach.
The Carrying Capacity was way less on the 340. Some are close to capacity right from the factory. Some of the things that affected the carry capacity were the following:
1. Allison 2500 vs 3000?
2. Tire sizes 255 vs 275 or 285?
3. Front air bags smaller on the 340?
You may also find that the hitch is 5,000lb on the 340 vs 10,000lb