We put over 100,000 miles on our 2001 gas powered motorhome (Ford F53 chassis) pulling either a Jeep 4 down or a Buick on a dolly. It went to Alaska, Newfoundland, Florida, California, and every place in between. Power was never an issue even on the steepest of inclines. It's gone through the Eisenhower and Johnson tunnels (7% grade) on I 70 more times than I can count. It went in and out of Skagway Alaska which is a 12% grade for 12 miles. It went through the Icefields Parkway in Alberta which has several stretches of 8% to 11% grade. Never once did we have a problem.
We now have a 2013 gas powered motorhome (again a Ford F53 chassis). It has over 17,000 miles on the odometer. Almost 12,000 of that was going to Alaska. It's also been to Florida, and just recently to North Dakota, Minnesota, and the UP of Michigan. All the time pulling our Jeep along behind. Again we've never had a problem.