Having driven the Badlands (both North and South Dakota) as well as up to Mt. Rushmore I hate to say it, but I think you're wishing for something that might just not be possible. My bus has 185 hp and 474 ft lbs of torque. I would imagine your DT360 would have slightly more or perhaps about the same amount of power. Pulling far less bus and no trailer up to Mt Rushmore and I was topping out at about 25-30 which was plenty fast for me.
However, if you wanted to make some more power it is pretty easy on that rig. Just remember that fully loaded with people, full tanks, and that trailer you might be pushing the limits of what that Allison wants to do and bumping the power up isn't going to make things any better.