I have some questions and your 31 posts since you joined did not shed much light on your situation. How old is old as you left that bit of info off. How many days a year will you use a RV? How many miles/year going forward do you expect? Why a diesel for that short a MH? Do you have a car that can be towed four wheels down? My concern is that you are now going for your third RV which may be too short for your future needs.
Major repairs at a truck repair place.
Previous to 04 I'd say no difference Cat/Cummins. After 04 Cummins and both will have the very good Allison 3000 6sd double OD tranny.
With an exhaust brake... never need a brake job.
Older than 10 years then yes change. If five years change only the serpentine belt.
Most change tires at 5-7 years. Having put all the miles on mine I went 7 on the front and 10 on the rear... $500-700 depending on size.
Unless you hit the steps, do not worry. A DP can have more systems than you might think.
