I just put a new 350 ho in my k-5. The problem I am running into is that when I drive it or even when it warms up fully the temp gauge reads all the way to the red. I have tried 3 different thermostats, and 2 different sending units. Both of which are now ac delco. Even though it acted the same with all of them. THe temp still rises. I ran it down the road without a thermostat and my gauge read on the first line and never left it. BUt when the thermostat is installed the temp wil go really high and then drop all the way back down to the cold mark. Another thing we did was run it with the cap off to get the air out, and also vacuumed out th system. I do not believe there is any more air in the system. We put a infared thermometer gun on the side of the block, both sides and the sending unit and at operating temp it always read about 200-220, usually. I never saw it higher than that even though the gague reads it really high. I am really at a loss here and I do not know what else it could be other than maybe the wire shorting out or the gauge not working. Even though that doesn't explain why it temp never went up with the thermostat out. Any help would be greatly appreciated!!!