I had to axle flip my fifth wheel, which gave me just under 6" of lift, to get it to sit level with my Ram and have adequate bedrail clearance. That's on the stock 33"+ tires. 35's would probably be doable but on my setup it would decrease the bedrail clearance and make it ride a bit nose high. I could always lift the trailer more but it's already pretty high as-is.
The other thing with the bigger tires is it will effectively lower your rear axle ratio. From a power standpoint it probably wouldn't matter with the Cummins but you'll probably see more frequent downshifting. I'd also expect your fuel economy to drop a bit with larger and heavier tires.
