omc 5.7 low rpm's underway

title says all. i am a engine man not so much boat. My boat is a 26' wellcraft 1984 aftcabin. My engine runs like a screaming eagle in test tub. but in water under way will olny go to 1800 rpm's. doesn't miss or anything can run like that all day. doesn't overheat perfect oil pressure. have dual point distributor so no advance, new plugs,coil, new carb with matched spacer. tried diffrent prop today but hit ramp bottom leaving dock so top performance was issue but still no rpm. bottom of boat has no groth i keep on trailer, paint could be nicer but not that bad olny a few chips missing on outer most layer.
I am really pulling my hair out Help!!!

There must be some mechanical timing advance built into the distributor...test the timing at idle and then at 3000 RPM..it should change. I am not sure of the exact timing advance but at 3000 RPm it should be at least 20 to 30 degrees BTDC

yea that is what i would think, but the points are mounted to the base, it has no plate that the mechanical advance controls. i am going to replace the plug wires this morning my pull distributor to get closer look. am thinking of installing a hot spark module, but the dual points are hard to beat.

replaced distributor to no availe.