sorry I didn't say it but that is a great looking rig,
I have heard when you run propane you are down on power about 30%, with us being already higher altitude that could mean even less power but I am no expert.
the npr's with the exception of the diesel model has always been a GM powertrain, and that was one of the big problem areas. the motors were done at 100k and the trannies blew every 30k. we had 5 npr's 4 gas one diesel these were replaced about every 4-5 years during my time there I bet I drove 8 different npr's, the gas models got 7 mpg on a good day and the diesel got 16mpg most of the time. the one diesel we had was the most reliable and it didn't have trans problems either, good luck and don't get stuck in the snow because only one set of dual rear wheels will spin and unless you are extremely careful you will blow the spider gears out of the rear end, I personally grenaded 3 rear ends getting stuck up in park city in the winter, 2 grand a pop. I even had one catch fire while driving it, we put out the fire with a pump sprayer and microban.