3.0l looses power on top end

[Fordrulz]

Hi guys new to the forum. I have a 93 mercruiser 3.0l Engine will idle all day long when you go to accelerate at wide open throttle then it will come up on plain and run good for 5 seconds then it will lack power and almost stall. If you run consistent at 3200 rpm it will run pretty good until you turn and put a load on the prop and then it dies out like it's lacking fuel. After running for a while the boat wouldn't even get on plane and lacked power worse than when the engine was cold. I did bypass the fuel tank and lines and use a regular tank to the pump for a fuel supply and it did not make a difference. The fuel is good installed a new fuel water separator filter and the caburator has recently been rebuilt. Not sure where to go from here maybe check fuel pressure? Any idea the best way to tap into fuel line?what is normal fuel pressure? Any help would be greatly appreciatedqo thank you