Power Issue on PCM Inboard

1996 PCM Windsor 351 w/ GT 40 Heads and Multiport EFI

Question: What might be causing older Performance engine with new engine block to have trouble powering to full strength with full throttle, when otherwise running smoothly?

Data points:

2 winters ago, extended freeze cracked block and exhaust manifolds. Purchased rebuilt block and manifolds from reputable dealer. Recently completed installation of rebuilt engine. Past week, ran great in driveway several times with water hose hooked to cooling system. Presumed we were home free and took to lake yesterday. It started and ran great out of the marina’s no wake zone. I full thottled take off and imagine my disappointment when it would only go to approx 2200 RPM...about enough to get planed and nothing more. It’s like someone put a governer on the motor to make it a smooth but boring ride!
Fuel Pressure: Bought pressure gauge and tested EFI. Getting 40 psi at schaefer valve on rail. This makes me think to look elsewhere. Two other tidbits: (1) I didn’t get to test if pressure dropped as I went full thottle. Will try that this weekend on the water. (2) I think this is a distractor, but will mention anyway. We were uncertain if air in injector rails would degrade performance. So we did a bleed at schaefer valve…surprised we got a small, but detectable pickup on performance…it kicked up to about 2600 RPM and we got a little pickup in power…not sure if this is important or not.
Throttle / Linkage: I did check throttle linkage to verify connected and fully engaging the thottle body. It was. Then I removed the Flame arrester so I could look at actual flapper valve on inside of throttle body and verify it was opening 90 degrees. It was.
I have put new plugs in before taking out. Have not changed rotor/cap/plug wires. Hesitate to do that now before I eliminate other more likely issues (the motor is running so clean, I don’t think I’m having problems there).
My sense is that either I need to have timing set and/or there is something happening with computer management of fuel / air / ignition mix that I won’t be able to find.
Anyone who has advise on this would be very much appreciated. Thank you.

You are going to need a fuel pressure gauge to start. Get one, hook it up and take a reading while running.

Thank you, Chris. I have one, it reads 40 PSI running at idle. I plan to test pressure this weekend on the water with throttle down. 2 questions:

1. If I start in my driveway and run revved up idle, is that a valid test...or does it need to be full throttle?

2. How much of a pressure loss running wide open would you consider to be normal (below which we change hi pressure pump).

the engine needs to be under load to conduct a valid fuel pressure test...

there should be very little pressure drop going to full throttle...the exception would be if you have a manifold referenced fuel pressure regulator.

My info suggests more than a 3PSI drop under load indicates replacement of hi pressure fuel pump. Tested in driveway today at high idles and lost about 2. Full test on water prob Thursday.

Also, found out that what I am describing is common to limp mode that can occur when Temp Sensor / Oil Switch / Ping Detection devices go bad. I will be testing all that on next water run.

I will address Timing if I get the chance but do not expect that to be issue for this problem...just something to get me to full power.

For my test, I will have a new pump / Temp Sensor / Oil Switch handy to try and close loop, and return what is not defective. Will follow up later in week.

Thanks for all the great advice.