Gauge Reads Hot, Rad Temp OK???

I just fired up my 440 for the first time since the rebuild. Break in went great but the dash gauge in my 69 Barracuda slowly climbs to 3/4, so showing very hot. I stuck a thermometer in the rad and coolent looks to be circulating at around 170-175 with 180 thermostat. During the build I put in a new temp sending switch (small brass one) into the front of the water pump. I was thinking that the sending switch was telling me the engine is hot but the rad is cooler meaning the thermostat wasnt working properly. When I run the engine up to where I dont feel comfortable with the gauge reading hot, I shut it down. The block doesnt sound like its as hot as the gauge looks. I'm stumped.......anybody got any ideas?? Thanks for your help.