Hi Airplane Joe,
Is your Cummins turbo-ed? If so, it will handle the hills like a breeze. As to maintenance, I would make sure that all the fluids have been changed when necessary, as well as the fuel filters and dessicant filter for the air brakes, etc. I just recently purchased a low mileage 2005 Safari 40DP myself, and the fuel filters & desiccant filter looked original. I've found that when you buy a used rv, most of the time, unless you get good records on it, you should change out the fluids, including on the generator, to have a good starting point. I did all of this on my "new" one, and just came back from an uneventful 3,00 mile trip. The Tiffins are well built, top quality units, and should give many years of trouble-free service.
Mike