Weird Evinrude 60 hp problem

[txgunslinger]

I have a 1986 Evinrude 60hp. The Vro has been removed. I let it set up for over 2 years. I recent remodeled the boat and installed three carb kits. It started and ran nicely in the pond here at home. I would run it under full throttle on the trailer and it would not miss a beat. I took it to the river and hit the throttle and it came up on plane and ran for a half mile at 5500 rpms then started to alternate from 4500 - 5500 rpms cutting out then back on and so forth. And it eventually just falls off plane and will only run at idle. I have rechecked/ recleaned the carbs, replaced all the fuel lines. Changed to a remote tank. Tried to choke it and it makes no difference. Tried to pump the bulb and no difference. Changed the coils, power pak, still no help. disconnected the temp sensor no change. QUESTION, could it be the ignition trigger? HELP

Thanks ALL

TX