Engine temperature gauge

[Touchdown67]

I have a 65 C10 with factory gauges and a SB400 engine. The problem I am having is the temp gauge goes to almost full hot after about 5 mins run time. I have gone through everything (ie. radiator, water pump) I put in a 195 degree thermostat instead of the 160 it had before. We have checked the temps on all the hoses and the water neck with a temp gun and the temps seem to be between 171- 195 degrees. I bought another sending unit from NAPA and the gauge still shows hot. I am wondering if there is a different sending unit I should be looking for or is the gauge shot. Has anyone encountered the same?