Stumped on hot temp gauge reading

[spacepirate]

Hey guys,

I have an LS3 with an Entropy radiator in my 68 Camaro. When I bring the car up to temp the gauge keeps steadily climbing to almost 250 degrees however when I use my infrared temp gun on the upper hose it reads approx 150 degrees and the lower hose is right around 110 degrees. I replaced the thermostat this morning hoping it was that but its still doing it.

What's weird is I've cruised it around the neighborhood and it doesn't show any symptoms of overheating, no leaking coolant, hot smell, etc. but still shows almost 250 on the gauge.

Anyone have any ideas on what to check next? Could it be a miscalibrated gauge?