1987 etlh 115 alarm problems/limping

Hi, have the alarm and limping problem. have checked and replaced all oil sensors/ control box and checked over oiling system. all is well there. changed impeller, checked and pee stream is solid, and not hot. cleaned tubes, and checked for any restrictions, all seems well. i can run fine full throttle for anywhere from 10 minutes to 45 minutes no problem, then it alarms and idles down. if i mess with the throttle for a couple minutes, it just takes right off and is good for 10 - 45 minutes again. 45 minutes is the longest i ride for when touring. also have checked fuel connections and all is well there. oil levels are good and continuously filling and being used. any other ideas?

Thanks.

charging system needs to be checked,battery cables clean and tight ,trim sending unit is it stuck up?contact dealer about bullitan on return to port module.

just a thought is motor over reving? does the boat have a tach whats your rpms. could wot timming to high?

check trim snd on engine. if stuck up push to down position