Note well. If you have ever lost the ground on the voltage limiter on the back of the gauge pc board, the most obvious sign of which is a fuel gauge that doesn't peg past F when you fill it up, both the fuel gauge and temp gauge will always read low.

There should be no relay switching or motorized valve stuff when you get on the gas from throttle closed decel. The heater water valve is above/right of the go foot, covered by a cone topped plastic cover held on with one screw. I'd make sure it's opening up all the way.

"Burp" the cooling system when you fill it up. Crank it and let it run up to op temp with the cap off (observe flow in the radiator top tank). I like to point the nose as uphill as I can. Raise the idle up by hand several times and see if it passes some gas. You should see the level drop as the idle goes up. I like to hold the idle high and cram in the last glug of coolant, and keep it high until I can get the cap on. Unless you have some kind of flow restriction, any air bubble should be purged over time as it gets to the radiator and is burped out into the coolant reservoir, and is then replaced by new coolant on the suck back.