Keep going. Good luck. i am hoping you find what the problem is. Same problem here. Older 90hp Mercury. Same as you, rpm's cutting back at high speed. I have had fuel pump rebuilt, replaced fuel lines, carburetors rebuilt, replaced 3 coils, sparkplugs and wires, installed new trigger assembly. I thought the trigger assembly would be it. There was a bad wire on it. Nope same as before, worse could not even get past 7mph. Next is the stator assembly and the switchbox CDI assembly. Keep this thread going, let us know what solved the problem. Also checked the fuel for water, fuel good.