1995 GMC Jimmy 1995 GMC Jimmy temperature gauge reading too

Hi, I have a 1995 GMC Jimmy. I have replaced the water pump and thermostat due to a percieved overheating problem. I have a snapon mt2500 that I hooked up to the computer. The temperature is running from 185 degrees to about 195 on the scan took. I replaced the thermostat with a 180 degree temp. No over heating. It is cooling just as it should. The gauge reads about 250 degrees. Is this a common problem? How can I fix this problem. temp sending unit? or different gauge cluster? Any ideas? Thanks -Ben