True Mystery: 2016 Mercury 250 Pro XS - Loss of Power but still running at 5700rpms

[kevinbryant1]

I have a 2016 Mercury 250 Pro XS, <Serial# 2B125759> mounted to a 2016 Ranger Z521.

Here is what the boats doing - Cranks up and sounds fine, however, she is slow to plane. Full throttle it reaches 52mph - Fully trimmed. The speed will increase a few mph on a long stretch.

The Complete mind bender is, the RPM's still read 5700. I have been questioning my eyes, as in "did i really see 5700? did i misread?" but i don't believe i misread the rpm.

The prop is a Fury, 24p. I have not checked the coils yet, but that wouldn't account for the RPM's. The only thing that makes sense, would be a spun prop, but i did not hear anything, and 52mph seems high on a spun prop.

If you have any ideas as to why this is happening, please let me know. Any help would be appreciated, i imagine this one will take some serious thought.