I have a 1988 merc 7.4L with bravo 1 outdrive. Everything runs fine around 2,000rpm 7.5 knots.
When I try to throttle up, the engine revs way up and the propeller stops moving the boat.
I've replaced the hub in my propeller several times and I have finally decided that was never the problem.

What else could be causing the loss of power transmission?
I've had good days when I can get all the way up to WOT, on plane, no problem and other days it won't push past 2,000rpm

coupler?

coupler

Haul the boat - Approx $ 200
pull the engine $ 200
coupler $ 400
6 hours labor @ $ 115

$ 1,500 seem about right to replace the coupler?

Do it yourself I did mine
Haul the boat 0.00
Pull the engine 0.00
coupler from cp 350.00
align motor 0.00
about 4 hours at the most in the driveway
Priceless

i dont get the 6 hrs labor listing???. you already listed...pull the engine for $200. once the engine is pulled, it's only 6 or 8 bolts to change the coupler. i can see if you listed re-install engine for $200, but where does the 6 hrs come from ?

Your total bill sounds right to me. A buddy just got a quote for a coupler replacement on a 382 Formula hp 500 for $1400.

i have had a rubber hub prop act like that also. it had a spun hub and it would hold up for awhile then let go. just my 2 cents. good luck.

Does the engine compartment smell like burnt rubber? If not, borrow a BI prop to test with. $0 cost