Loss of power at WOT at first

[Jamesfishing]

2005 mercury optimax 175 serial number 1B105692 it’s on a 2005 triton tr-186

I’ve owned the boat for 3 years now and the boat has ran amazing it normally runs 63-64 mph on full tournament load at 5600 rpms, it is now having a hard time coming up on plane and is now running 55 ish mph at 5000- 5200 rpms with same weight and some conditions but it runs great at idle. Here are all the things I have done to try and fix the problems I’ve changed the fuel line from the tank to the motor, I replaced the primer bulb, I changed out the fuel filter , I changed out the spark plugs with NGK spark plugs , I replaced the anti-siphon valve , I changed out the tracker diaphragm which was separating around the edges , I replaced the fuel diaphragm which had a cut in it,
I replaced low pressure fuel pump , tested compression on all cylinders all are around 118-120 and I’ve tested the coil packs and they are all working , I have hooked up gauges to the air side and fuel side and the air is 80psi and the fuel was reading 90psi so after changing all that stuff it still runs good at idle but in the water it won’t come up in plane and it’s like it’s not getting enough fuel after 1/4 of the throttle is pushed in and will cut in and out and sometimes dies however out of water with it hooked up to a water hose it runs like a brand new boat so I’m now at a loss on what the problem is any help would be appreciated.

[lpugh]

Need to get air fuel pressure on the water under load while it is acting up, also need the low pressure reading from the Shrader valve on the vst

[JOE54]

^^^^^^+1

[EuropeanAM]

+2... may also need to reference WHEN (at what stage) the plugs were replaced, as you've had problems you say you corrected that can trash a set of plugs pretty quickly.