280 Sundancer 4.3L port engine no power

Hello all, I hoping I can get some possible causes and solutions as to what just happened recently to my 2002 Sundancer 280 (twin 4.3L EFI (TBI) engines) engine has 418 hours on it. Running normal and on plane then out of nowhere Sync guage swings over to Port engine and I lose plane and port engine does not make any more RPM than 3000 which will not keep the boat moving enough. Checked for anything stuck in prop or prop damage (none). Got back to dock at cruise speed with no issues. At the dock engine idles fine, no back fire or miss and I have lots of RPM when not under load. Pulled the cap and found a bit of wear on distributer and roter. cleaned up with fine sand paper and reinstalled everything and took boat out no change. At WOT RPM just stays at 3000 but starboard is strong and will pull above 3000 no problem. After that and to summerize what I did in the last couple of days to here is what I have done: As an FYI, plugs were changed when I first got the boat (250 hours) boat is not overheating, fuel filter / seperator changed at start of season, oil pressure is good, air cleaner is clean, have full stoke of cable to throttle body. Checked code on ECM and only get 14 which is CTS signal is low (which it was as engine was cold at the dock). Unplugged CTS and took for a spin but no change. Unplugged air temp sensor mounted on flame arrestor and no change. Swapped MAP with other engine (no change). Ran resistance check on both TPS on both engines and they were pretty close on OHM readings from idle to WOT. Running out of options here now aside from calling in a pro. I have not done a compression test as the engine seems to run fine when not under load. Thanks in advance for any replys

Did you check fuel pressure? Don't rule out low compression in a cylinder - one of my 5.0s ran fine and smooth but would not go over 3k rpm......it had very low compression in two cylinders - looks like you're in fresh water, but was it ever in salt? have the manifolds/risers been inspected/replaced?

Ididntdoit thanks for the quick reply. Yes Im in fresh water (Lake St Clair area) but boat originally came from Florida in 2014 and yes I had to replace the manifolds, spacers and risers (along with thermostat and impellers) when I first got it. Yeah I'm hoping I didnt drop any cylinders but from what Im seeing now, Im losing hope. Thanks again.