340 overheating problem

It seems like there's been a rash of threads that I've been reading lately about temperature gauges that aren't accurate. I know that I've got a problem with my own. My factory gauge reads hot but I'm running a Mr. Gasket radiator cap that has a built in thermometer and it reads 180'. I used a portable infrared thermometer to check the engine temp and it agrees with the radiator cap so my interior gauge is off.