Good Afternoon, I've used the forum resources to research lots lately and can't figure out which direction to go. As the title states, I'm having overheating issues with a GT150. I took it out recently, idled for a while as I parked the trailer, got out past the no wake zone and opened her up to 3500-3800rpms. Within 2 minutes the overheat alarm went off. Let it cool down and limped it towards the ramp. No alarm till I opened it up again and within a minute it sounded. The telltale was a steady stream of ice cold water. It appears that at idle its ok. So I pulled the heads off and the water diverters were badly deformed and pushed through where they should be. Changed all 6 of those diverters and changed the thermostats and bypass valves below the thermostats for good measure. The only thing I didn't change was the rubber grommet that the bypass valves sit into because I wasn't sure at the time how to remove the old one. Took the boat out again and same thing, idles fine, overheats when I get the rpm's up. I haven't tested the exact temperatures of the heads yet because I didn't have my temp gun with me but its extremely hot to the touch so I don't think my sensors are bad. The water pump was changed this past summer and it was running fine all summer with no issues so that was installed properly and is only 8 months old. My question is where should I check now? Ive tried reading online and can't come up with any other items to check. I pulled the new thermostats out just to double check and they are working correctly in a cup of boiling water. I just ordered new gaskets for the water jacket cover so I can change the little grommets that I skipped before but I'm out of ideas and getting very frustrated. Water flows through the tell tale steady but is always ice cold. I normally run in fresh water and not shallow. No sand or mud issues that I've noticed but I flushed through different ports with air and the hose just to make sure. Yesterday as I was playing with it on the earmuffs, after putting the heads back on, making sure the diverters were still in place, I started it and the telltale started getting warm, hot and then right back to ice cold for the rest of the day of starting and stopping the motor. Unfortunately I can't replicate the overheating unless its under load but I'm hoping that maybe the scenario of the water getting hot then turning ice cold will spark an idea? At home at idle, the heads were right in the 140 mark like they should be. Please help...