Could be a thermostat going bad or sticking, if you can find someone with a heat sensor you can check everything, some bigger marinas have them.

That's the only other thing I could think was thermostat. Can one for any Chevy be used like from auto parts store? Or does it need to be from mercruiser and what temp?

A bad thermostat wouldn't cause low water pressure

Then what else could be the cause

Plugged hose thru transom

With both high temp alarm and low pressure conditions, you have low flow issues

In your pic, did you look at all the vanes and the full length of them to make sure they arent broken off inside the housing, vs just glancing at the end shot?

Yes tool it out and it's all good

Since it's apart I did order a new housing and impeller, water was flowing back thru the drive pretty well last night

Also check hoses for cracks...if you have an air leak, you could be losing suction.

True enough.

Do you have a freshwater flush system?

it would if it was stuck open. and not moving enough water to get it to close .. feel youre exaust if feels hot youre clearly not moving water .or enough water .. easy way to tell ..exaust will feel warm to touch not hot ... if moving adaquate water past the or through the engine ..like for instance running without a t stat it takes large amounts of water to build water pressure as ther is no restriction .. becomes a strait through process .. i had to lower my water intakes half inch below boat to achieve 15 pounds of water pressure without a t stat ... good luck