I wouldn't buy anything that size with less than 400 Hp. My rig came with the 350 ISL and it was fine but my GCWR is 35,000lbs and it was a little under powered on the steep passes. I had it uprated to 400 Hp and gained 200 ft/lbs of torque and it made my coach into a fire breathing dragon. Doesn't even know that it has a 4500lbs pickup truck tied to it.
Craig & Carolyn Roberts Apple Valley, CA
Toad: 2017 GMC Canyon 4X4 Crewcab