94 - 150hp 2-cycle wont go above 2200 rpms when it warms up

boat a new boat, well new to me... And well i got problems right off the bat.

It's a 1994 150hp 2-cycle.
So the issue is that when the boat warms up, about 15-20 minutes into running it, an alarm goes off under the dash and when that happens the engine will not get above 2200-2400 rpms and shakes pretty bad, it doesn't die. The first time this happened it was under load in the water, but it also would do it in neutral when i attempted to rev it up that way. It will also do it on bunny ears in the driveway too. Basically as soon as the engine is at operating temperature the alarm goes off and this happens doesn't seem to matter if its under load or not.

I have no gauges to tell me what the alarm could be... The water is spitting out of the engine in a nice steady stream, the oil reservoir on the engine is half full, the spark plugs aren't brand new but pretty damn close. When I took them all out they all appear to have the same amount of carbon build up, not too bad on all of them.
I tried removing the spark plug wires while its running, cant really tell if any of them aren't firing, i cant tell if its dropping rpms when i pull them. (is it very minor on these motors?) but it seems like they would be since when the boot is close to the plug its arching to the top of the spark plug on all the wires.

I don't know any ideas?

First thing, Is she over heating? Place hand in telltale stream, you should be able to hold it there indefinitely, Next place fingers for a 6 second count on either cylinder head, If fingers get scorched she'running to hot! A infrared temp. gun will do the same.That alarm is telling you there's an issue,Overheating,low oil,insufficient fuel/oil flow, Your engine is going into limp mode to protect itself from further damage, It's shutting down half the cylinders by orders of the ECU

Ok, thankyou I will need to try that today. Last night I checked the compression and all the cylinders are at 120

ok so it's definitely an overheating problem not oil. Checked the oil pump and it's all good.

I replaced the thermostats, the "starboard" side's thermostat was not bad but i still replaced it. The 'port" side had a lot of corrosion and about a 1/2 golfball size chunk of salt sitting behind it, replaced that one too after cleaning all the gunk out. (I did check the stats in boiling water and they did both open however...) either way there's new ones in there now.

Then I ran some salt away stuff through it with the whole thing sitting in a big tub and ran it for about 15-20 minutes, the telltale stay relatively cool the whole time. Seemed good, but when I put some bunny ears on and was just flushing it with clean water it sounded the alarm again at about 5 minutes.

I discovered that the temperature sending unit on the starboard side is the culprit for triggering the alarm, when i just tried unplugging it it turned it off and likewise turned it back on when i plugged it back in. It's a bit strange as that side of the enginer was alot cleaner than the port side.

So I don't know, what should I do next? Should I pull the heads so i can really get in there or is there something else I could do before that?

Also out of curiosity the two hole at the back of the engine, these are for exhaust right? Water isnt supposed to come out of them also? (because its not)
One of the attachments I uploaded is a picture of these holes...

And one last thing there's some sorta oil or grease leaking down the side of the midsection. Now im not sure if it's just flushing some crap out from the top of the powerhead or if this is yet another concern. It's a milking brownish color... I uploaded a picture of that too.

I appreciate your help

Running on muffs,possibly not enough volume of water,go back to tub to see if overheating issue subsides. Since desalting in tub have the RsPM increased, Not a fan of revving in neutral,no load on engine.