Hi Roger and everyone who replied!

Thanks so much for the constructive feedback!

Couple of points to clarify:
- I forgot to mention, the gear ratio is about 1:2.06 (can't read the
label on the gearbox)
- I recently had the bottom done completely - it is as smooth as it
gets.
- I also had the propeller checked by the manufacturer and they
confirmed that the pitch is what it has been manufactured at.
- I have a brand new shaft and coupler and these are properly
connected.

So, I guess my best bet is to check the transmission. Now, how do I do
that?
- Can I check the clutch/transmission without disassembling everything?
Any ideas?
- Can I check and repair the transmission without hauling the boat out
of the water?
- I also notice that there is a very high pitch noise from the engine
after about 3700rpm until the max. rpm. Could that also indicate a
toasted transmission?

Thanks again!
Dennis