1993 90hp merc carb fuel starvation issue

Help me with this motor.. I have a 1993 90hp mercury outboard 3cyl, compression is 120 on all 3 the thing runs perfect except for full throttle, it runs beautiful for 10 seconds consistently then all of a sudden it slowly seems like it starves for fuel and just sounds like its running on a couple cylinders. it does want to go though.. I bypassed the gas tank thinking it could be a venting issue, still the same.. i replaced all the fuel lines and filter, used an external gas tank filled with fresh gas changed primer ball, fuel pump was rebuilt twice thinking it was assembled wrong the first time but confirmed it was OK by two different marine techs. coils, power pack, stator and trigger were all changed. The marine tech made sure the sync and timing was good. He is very confident its a fuel delivery problem after i showed him a video of what it was doing it almost seems like the fuel in the bowl is burning out and just cant fill up fast enough to keep the high speed going. I tried pumping the ball while going full thinking the fuel pump can't keep up. what could this be????

could be low float settings in the carburetors, bad fuel pump/ fuel pump check valves.

Was this ever resolved? I have a 1989 90hp mercury 2 stroke with almost the same issue. I have installed a new stator, new switch box, rebuilt the fuel pump, new oil and fuel lines, tried an external fuel tank and hose, installed new reed valves and cleaned the carburetors. All the jets have been out of the carbs to make sure they're clear. The carbs were soaked overnight in carb cleaner. New spark plugs and new fuel also. It starts and runs great in the driveway. I get to the lake and it is really hard to start with the motor submerged in the lake. But it idles great when it's started. It just will not go full speed. It will go about 20 mph on a 18' aluminum lund boat. If I put the throttle all the way down, it boggs down to nothing. But if I keep it about 2/3 throttle, it will go about 20.

I did get it resolved, I basically did the same thing you did rebuilt fuel pump cleaned and rebuilt carbs all the above.. It turned out to be the silliest mistake i made when i put the fuel hoses back, I accidentally mixed up the two hoses that connect to the choke i had the main feed on the wrong nipple, so the carbs were not getting the right amount of fuel. When the marine tech switched them around it ran like a champ. It is a very easy mistake to make even tho it looked like it was hooked up right.