Risers aren't new but they had very little crud in them if any at all. It seems to flow plenty of water. It's just got me baffled. Is it possible the circulating pump is failing or weak and can't keep up with higher rpm?

its possible, though usually they leak out the weep hole on top when they go

It's an alpha drive and it's been run on the hose a good bit. Would the impeller even tho it's new cause this kind of problem or would a bad impeller be obvious at other rpm as well

Will it heat up if you're running on plane around 3000-3500 or only wot.... You could try to change out the hoses with clear ones to check water flow

It's fine at cruise speed around 3500 rpm but as soon as throttle is opened it starts to heat up with in 5 to 10 seconds and after about 45 seconds at wot I have to throttle back and it cools right back down

Are you sure the gauge is accurate

If you're sure that the impeller and water pump housing are in good shape, you might backflush and clean out everything carefully - amazing what some old pieces of a prevous impeller can do if lodged say in the neck on the transom assembly... restrict enough water that when you turn up the heat it can't keep it cool...

In addition, alpha water pumps are a little touchy. If the water pump housing has grooves in it, etc... it can significantly reduce pump flow.. so can overtightening the nuts holding the water pump on... or a kink in the line fromt eh drive to the transom assembly.. I know it's a pita from experience. Hope you figure it out soon!

When we took the old impeller out it was intact but was just brittle and not keeping cool at idle last year but was fine at wot, but that was the old engine that only turned 4100-4200 rpm, maybe the housing is worn out but didn't show itself until it got something with some ass behind it. I will recheck all of it again when we pull the drive back off

99% sure, but I would be willing to check it, is there a certain test for the gauge other than replacement?

Ok I just had a thought and I want to see what you guys think, when we first started the motor we set the float levels down a good bit because it was trying to flood when we were priming the fuel pump, now I'm wondering if maybe it's a fuel problem but not because the jet but because it's sucking the rear bowl dry after being opened up. It's a standard bore 350 with a 650 demon carb. At idle the fuel level in the sight glasses is between 1/4 and 1/2. I'm thinking that maybe in fact it's running the bowl out of fuel and just misting enough to keep it running but not cool.