Sputtering out after high speeds

so this weekend we took the boat out. after wakeboarding for a few hours we brought the boat back to the dock to empty the fat sacs for skiing. took about 30 min or so. after about an hour we got back in the boat for some slalom. after 15 more min i pulled my friend out of the water just fine and was getting up to speed, at about 25 mph it would just misfire and wouldn't let me go any faster. this happened every time we tried to accelerate past 25. it will hold at 25 and run perfectly normally, but anything past 25 it misses badly, i am new to slalom and it was my first time out for the season, so i just wanted to practice getting up, after a few attempts i got up and the boat ran perfect i got a few passes in at 36 mph, we swapped skiers and we got a few more passes in, and once again out of no where it started missing and we went back down to 25. ill try to get some pics today. but it seems to be getting worse.

any suggestions?

electrical?

Fuel?

Spark plugs?

so to answer your question, im not really sure. there is a distributor, so i guess points. but the spark plugs don't plug into the distributor, there is a wire harness that attaches to the distributor that runs to some kind of coil maybe? and then the spark plugs attach to that.

Is it points or electronic ignition?

My finger would point towards the coil or the ignition pickup (if it is electronic) getting hot from the higher spark rate then cooling back down after it runs lower rpms for a while.