You gearhead race car people sure make me laugh. It's torque that turns the drive wheels and HP is only the potential output of the maxed out RPM engine's capability.
Just a little hint: Normal people don't tow their RV down the road with most modern gas engines spinning at 5,000 or 6,000 RPM's! Therefore, the max rated HP capability is virtually meaningless unless a low gear is used with the go pedal to the metal being required for max engine RPM output to move the load at the speed desired.
I wonder how many of you ? RV'ers would like to or would pull your RV at 5,000+ RPM's constantly so you could even use the max engine rated HP?
A cheap little 5 HP gas lawnmower engine will propel a 25,000 lb MH up a 6% 10+ mile long grade with it running at max RPM's like 3600 and geared down properly to the MH's drive wheel to provide the torque required to turn the drive wheel and move the load up the grade. Of course, the engine life will be shortened drastically just like a vehicle engine would be turning 6,000 RPM's constantly.