Low RPMs at WOT

I've been running my boat for a couple years like this but really don't think it's running full strength.

24' Pontoon, 2002 90 HP TLR 2 Stroke.

Symptoms.
- Max RPM is 4000 at WOT. 13 MPH with just a few people on it.
- Max RPM is down to 3000 if I have put a lot of people on it. Goes about 5 MPH.

Other than that it runs fine and has been reliable.

Things we've tried.
- Replaced Plugs
- Carbs cleaned, let them soak for hours. Never found any issues inside the carbs. Looks clean and jets were clear.
- Replaced Fuel Filter
- Replaced Fuel Pump
- Bypassed fuel from tank and went straight to fuel filter from a different fuel tank. Ran the same.
- Compression is 120/110/120
- Checked Spark, all 3 are firing. Got shocked finding out.
- Linkage I THINK is correct? when put into WOT the carbs turn perpendicular.

Haven't replaced the prop but it ran faster before so I don't think it is the wrong kind of prop.

My water pump is due for replacing and while I took off the lower unit I saw a damper seal was pretty corroded. One person online with a mercury said that he had the same symptoms and his exhaust was somehow backing up and choking the engine at higher RPMs. I'm not sure how important that damper seal is and didn't know if it could be causing a similar problem. I looked up the mid section of the engine and didn't see anything clogging exhaust.

Any other ideas?

Water test At WOT with light load and calm conditions. Spec rpm range for your motor is 4500-5500. Prefer to be at top end of range. Assuming the engine is running at peak performance, if your not hitting top end range then likely overproped. Also check engine height.

I have little confidence that the engine is running at peak performance. I don't think it's over propped or just an engine height issue because when I first took it out it ran at higher RPMs. Somehow the linkage for forward came off and we repaired that, and ever since then it hasn't ran at higher rpms.

WOT with light load is usually 4000, sometimes not even that.

I can consistently replicate power loss. I got it on video. At 5 seconds into this video I'm extremely slowly pushing the control level to give it more power, and once it crosses a threshold it loses around RPMS and power. Once I cross that threshold I lose a few mph and probably around 600 RPM if I let the boat settle. You can see at 14 seconds in the video the RPM kick back up quickly, but all I'm doing is pulling BACK on the throttle ever so slightly.
https://www.youtube.com/watch?v=lAD-N8CUeIw

I noticed my linkage on the CDI is right at the tick marks that show II when I cross that threshold. I don't know if it's supposed to go way past that like it currently does because it seems when I cross that barrier I lose power. I also noticed that the plastic piece that connects to the CDI has split so is it possible that my linkage to the CDI is causing that? It definitely still moves it still even with the crack in the connector. Can I adjust the CDI linkage without possibly hurting the engine as a test?

Here's a pic of my linkage for the CDI. In this photo I have the controller about half way forward, around the spot that I lose RPMs. What do those notches that I'm at mean? When I got WOT it actually goes all the way over to the left where I have marked "WOT?"

Fixed it!

For those who ever have the same problem, this is what happened. Someone set the linkage "Stopper" so that the control arm went all the way forward. This caused the linkage to the CDI to pull way too far, all the way to the left side in that picture. I adjusted the stopper so that the linkage to the CDI stopped at the II marker even when I go WOT. I saw someone a picture of someone else's engine and it looked like how mine is set now.

Got back out of the water, and she blew past the 2300 RPMs barrier that kept bogging the engine down. I couldn't find much info on the CDI and how the linkage worked so I don't fully understand what is happening when you go past the II marker. It sounds like it goes into some kind of safety mode but still could occasionally get up to 4000 RPM. I don't know, but what I do know is that now it goes to recommended RPM and I'm happy about it.