91 Comp, GT40 heads, 1992 Ford 351 PCM ignition (High Altitude specific package). Boat is at 8200ft. @800hrs. New carb, not jetted specifically for altitude. The boat is misfiring intermittently at @2700 and 3200prm. It was doing so prior to the carbs replacement. Does this sound like a timing or advance issue? The reason I question the timing/advance is my 87SunSport has the same carb, same jet, and runs fine (a little rich), on the same lake. Treated gas, changed fuel filter, checked all plugs, wires and no love. Any thoughts or suggestions?