wow, well I had to go look it up, this must be a bsse model XL or XLT to have 17" wheels. Honestly I had no idea they even bothered anymore, still if you are looking at new just get a 350. Had I known I would be towing a 5th wheel I would have skipped the 250, yes I got a great deal on my truck and im certain they are trying to make you one also since most people skip to a 350.
BTW...I have 90k miles on 6.7 and it has been a great engine, yes the older 6.0 was known for issues.