1999 150 hp 2 stroke loses power while running at high speed on plane

I have a 1999 150hp 2 stroke Outboard engine Model# c150txrxon on my cobia that will not stay on plane after about 5 to 10 minutes, engine starts to lose RPM engine sounds rough and has vibration. Pull throttle back to idle, throttle back up will run a couple seconds on plane then does the same thing. The engine runs fine for hours out of gear at any rpm. Had engine in shop, checked fuel system, cleaned carbs, new plugs, fuel pump, new water pump, new fuel line. $1000 plus work. Took boat out and same thing is happening. At a loss for what is wrong, this engine has ran since I bought the boat in 2008, just needed water pump, plugs and water fuel separator. Running on ethanol free gas. I have a couple videos of the problem happening if I can figure out how to post them. Thanks for any help. I don't think it is fuel supply because it runs good for about 5 to 15 minutes before it fails.

1999 Yamaha 150 hp 2-stroke model c150txrx. Engine stalled out wot, acted like out of fuel which I believed was the problem since the fuel gauge said empty. I tried restart several times no go. Continued to fuel dock with kicker engine. Just had this engine in shop for losing power on plane wot, mechanic replaced all fuel lines, found water fuel separator full of water which was replaced; every thing was running great, mechanic took boat out and ran over half hour with no problem.
So back to the latest problem, at the fuel dock put 6 gallons in the tank. The engine finally started after several attempts, pumped up primer bulb several times before engine finally started. Engine mechanic at fuel dock said engine had ran out of fuel, hard starting was because it took several tries to fill all six carb floats. Pulled the boat went to fuel station, this boat has a 100 gallon tank, I put 6 gallons in at the fuel dock, the pump quit after loading 29 gallons. Fuel gauge now shows full, verified that by pulling the fuel sender out, fuel was maybe 1 inch below the top of the tank. The weird thing is I have a 100 gallon tank, only took 35 gallons counting the 6 at the fuel dock. This sender has a gauge on it that shows full, so both the dash gauge and the sender show full. At the time of engine stall the dash showed empty, never looked at the sender gauge to verify the two were showing empty.
Took the boat out last Tuesday, ran to the same spot we went to when we had the engine stall, engine ran great the whole trip. Loaded the boat on trailer and went to fuel station, only took 5 gallons to fill after 14 mile round trip. That sure looks like pretty good fuel consumption. I have pulled the fuel pick up and anti-siphon barb, both were fine.
I'm just puzzled that everyone at the fuel dock was certain that I had ran out of fuel yet it only took 35 gallons to fill the tank. What the heck would have caused the engine to stall like it was out of fuel though evidence shows that never happened. The last time out the engine never quit after traveling the same distance traveled. I am stumped, any ideas guys?