I apologize for not posting what I found the problem to be. That was my biggest pet peeve about this site is there are a lot of solicitations for help but when the problem is found the post dead ends with no fix listed and that is exactly what I did. I have learned the hard way that the high pressure pumps have a serious issue on the North River jetboats with the 8.1L (and many others). Long story short, after replacing the high pressure pump with a used "spare" that came with the boat and having the exact same problem, I ruled out what indeed the problem was. Apparently these pumps have an extremely high failure rate, especially if you are sucking air, the cause being a minute air leak on the suction side or in my case of parking the boat nose low in the driveway with a near empty tank after a trip and having the fuel drain back to the tank to where even after filling up the high pressure pump ran long enough pumping air that I ruined a second one last week. I ended up buying a fuel pressure gauge to narrow down the problem and found that my pressure dropped off when I was in the higher RPM band, hence my 3600 RPM max. This pressure should stay constant and honestly I don't remember what it was. It's been so long that I don't remember the website I went to for diagnostic of the engine (marinepower.com maybe??), it was great! step by step diagnostic..... however, I do know that the part about the fuel pressure is incorrect, I think they cut and pasted from the automotive application which uses different pressures. According to the diagnostic my pressure was right in line (at the lower RPM's, I didn't figure out the drop at higher RPM's until later) .....for a Chevy pickup. Hope this helps someone......... Charlie