'89 Evinrude 90HP V4 VRO Won't Rev out WOT

'89 Evinrude 90HP V4 VRO.
Model# E90TLCEM, Serial# QJT650961607

I was out running at full throttle, engine was running fine when suddenly the engine acted like the throttle was pulled back to just above idle (5 MPH). Limped home, called mobile marine repair guy.
Here is what he has tried so far over the last two weeks:

1. New spark plugs
2. Compression check - 120,120,120,119
3. Timing base (from known good motor)
4. Stator (from known good motor)
5. CDI unit (from known good motor)
6. Checked for broken carb reeds
7. Checked butterfly valves opening fully
8. Cleaned carbs
9. Hooked up remote fuel tank
10. Installed new propeller (old one was damaged)

After each one of the changes above, the engine was tested with the same results. The above has improved the situation slightly (prop probably made the biggest difference), and the engine starts, idles and sounds good and will get up on plane but it continues to feel like I am only getting 60-75% of throttle from the motor. I've had the boat / motor for several years and I can feel that it just isn't topping out like it should.
Any thoughts or suggestions appreciated.

Test run with timing light hooked up to 1 cylinder at a time.----Look into carburetor bores with a strong flashlight and compare fuel amount coming up the main nozzles.----Check for a bad plug wire & boot arcing to the cowling latches.