99 Tahoe: Thermostat gauge rapidly rises as soon as i get over 90kmh.I let off and can watch it go back to where it normally sits. It doesn’t seem to have a coolant leak and is topped up and im not sure if it was actually hot when the gauge rose but im thinking its the gauge itself that's the problem. I was only driving for a few minutes before i noticed it and my heat was blowing cold air still, even cranked to the max like it usually does when its not fully up to temps. Lots of talking sorry just looking for other opinions before i start tearing things apart and if i should be worried about overheating it