We have a 2002 Itasca Horizon, 32' DP with the Cummins 5.9 300HP Turbo diesel and the Allison 6 speed trans. It has an exhaust brake. Yes, there should be a switch, probably a rocker switch, somewhere handy. Great engine and transmission. The exhaust brake works well with the Allison cruise control.
I'm not sure when the 5.9 was first upgraded to 300 HP. This is something that you will have to check into if you don't get an answer here.
The Freightliner chassis is great, and yes, any truck shop should be able to deal with it, though we tend to keep an eye out for Freighliner shops.
Ours has about 100,000 miles, the wear and tear tends to be on the RV stuff rather than the mechanical, though we have had a serpentine belt fail in Mexico, and the injector pump failed in Eastern Canada. We had a transmission fault which turned out to be a wiring problem due to vibration. This too was in Mexico and an Allison service truck sorted us out. BUY AND CARRY A SPARE SERPENTINE BELT. It cost us hours trying to locate the right one!
With a DP you will have Air Brakes. Best thing ever. BUT even if not mandated in your state, take an Air Brake course anyway. You will save yourself some worry and possibly $$.
Don't buy a DP because it gets better mileage than gas. maintenance will cost more, though you only need to change the oil once a year. Buy one for the comfort, ride, handling, Allison trans and the air brakes.
I wouldn't buy anything without a test drive unless it came with an iron clad 100% money back no fault guarantee.
