I've had 2 gas motorhomes, and 3 diesels, and I'll share my opinion with you. My current motorhome has a 350hp Cummins. As far as climbing a grade, your gas rig will do just fine. It will probably keep up with the diesel, and in fact might even be a little faster (just a couple mph difference if any). Going up a 6% grade, you'll do around 45-50mph......give or take a little. Most grades are only a few miles long anyway, so a little difference in speed is not a big deal, one way or another. The big difference is noise. The gas will down shift so the RPM's increase and fans will come on to cool the transmission...........it will be so noisy, it will be difficult to talk. The DP, will down shift also, but the increase in noise is barely noticeable. That is one of the advantages of a DP. The other, is going down the other side of the grade. The exhaust brake makes brake usage minimal. My motorhome is an 04, it has 40k miles, and is in very good condition. I've owned it 2 years now. I've had to replace the lift pump, Electronic control module replaced, and just the other day, had an air leak, which was the left side ride leveler actuator. I also had to have the plastic engine coolant tank replaced. I did buy an extended service contract (extended warranty) which has helped, my out of pocket expenses on these items was approx. $1400. Oil changes cost about $250 at Speedco, and can cost several hundred dollars more at some shops. My gas 8.1 Workhorse Chevrolet use to cost about $60 for an oil change. The cost of the DP is a little more.....but the ride quality and the lack of engine noise is well worth it to me, and I know many out there will agree with that. With new tires, batteries, and good overall condition of the unit your looking at, I'm sure you'd be very happy with it, but if you decided to keep your gas unit, don't worry about grades, it will do just fine, just nosey.
