Yes, I agree. Definitley higher at 4K RPM's. Top end on this boat is mid to upper 30's. See what happens next year.Even with it cutting out I would think 4000,rpm would be faster than 23mph. Should be in the 30 mph plus range, unless something is up with the prop, he's 7 to 800 rpm short that boat should do close to 40 mph
Coupler - keep bumping the engine over (flip the kill switch) till you see the zerk. Yes, space is tight.
Gimbal bearing - on the outside of the boat, on the stbd side of the piece that is actually attached to the boat (transom plate) there will be a zerk.
Tilt/lock - this is the easiest one There is no such thing on a stern drive - that's an O/B thing.
Pull the prop off and grease the shaft.
Did you use the antifreeze that has propylene glycol in it (and not ethyl alcohol)?