I have a 5.0 MerCruiser MPI with Alpha drive. The recommended rpm range is 4600-5000 rpm at WOT. I had a 17p Vengeance prop and was going about 52-55 mph at 5200 rpm. I just switched to a 21p Enertia and am impressed with this prop. Now, I'm doing a little over 60 mph but, my rpm's dropped...