We've owned and towed with both a gasser and a diesel and it's diesel all the way for us due to the loss of horsepower at the higher altitudes in Colorado (~4% per 1,000 ft gasser/ ~1% per 1,000 ft diesel).
We'd much rather arrive at 10,000 ft having lost only about 10% of our horsepower in the diesel rather than the ~40% horsepower loss in the gasser. I'm not sure, but I suspect a turbo-boost gasser would do better so it might be an option if it had the needed payload capacity to haul the hitch weight of our 5ver (~1,750-2,400 lbs) and all our gear/passengers.
That being said, if we weren't pulling in the mountains all the time we would have to reconsider the cost aspect of the diesel versus the gasser. But, since we do pull in the high country almost every time we pull, we'll stick with the diesel. Also, the exhaust-brake feature on our new diesel is one I can't wait to try out.