Evinrude Problem (Need Help)

[sooner]

I have a 1996 Evinrude 115hp outboard. The motors runs great when you first unload the boat and take off. It will run 5 or 10 minutes, then starts running rough and slows down to 2500 RPMs. It will not go back to running good until it sits for 1 hour plus. The audible alarm never sounds. What might be causing this. I removed the thermostats and tried it and the problem did not go away.

Thanks

[ChampioNman]

Got a water pressure gauge? Does the audible sound when the key turned on? Last time a water pump been installed? Head temps? Good discharge out of the tell tale?