I guess it actually depends on how many miles you go each year. Do you really want to pay for a new $50,000 truck to go up a hill 10 MPH faster with the 7.3L gas engine? Or stay with your current truck and take a extra 10 minutes on each trip?
As for the diesel engine option, while you will get a little more money when you trade it in 10 years, the difference is probably not the $10,000+ more you will spend to buy the truck this year. So if you drive a LOT of miles, a diesel can be a little less expensive for fuel, but not for oil changes, and other yearly maintenance, and especially insurance costs. So if the diesel is costing about $50 more a month to buy insurance, are you really saving money? And yes it will go about 10 MPH faster up those few miles of really steep hills. So you will save about 10 minutes on a 3 hour drive?
Personally, I think I would stay with the 6.2L that is probably already paid for!
I bought a brand new Bounder class A back in 1997. I put on about 45,000 miles in 16 years. If I had paid more for a diesel, I would have saved a little on fuel, been able to have a longer RV, but not saved on oil changes! I am very satisfied with my gas motorhome. It served me very well, and I even lived in it for about 8 years. When I took a cross country trip, twice, the fuel was expensive, but acceptable. I don't think a DP would have been less expensive to drive. However insurance was much lower cost, so a lot of savings there.
On my trip in 2005, I was estimating about $0.50 per mile to drive the RV, so I kept the trips as short as possible, but still see what I wanted to see!
Have a great time deciding what to do!
Fred.