Gauge Reading hot but its not.

[68 Greenie]

Okay guys its Greenie again with the same issue. I bought a thermostat housing with a hole in it to put my temp. sensor in it. I bought a new temp sensor at Napa its a Proformer one its one for our year and its still making my gauge go nuts. I installed a new Edelbrock 750 (had a 600 performer) because I thought it might just be running lean and the shop that built my 383 recommended i step it up to a 750. My radiator cap that has a temp gauge in it says its at 150 along with the gun it shows 152 but my gauge just climbs up and up and up. I have a new aluminum radiator with cooling fans and it worked great along with my gauge with my stock motor. Please someone help me.