97 Yukon Temp Gauge Jumping

I have a 97 Yukon 4wd 170,000 miles. My temp gauge started to jump like it would work, not work. It would work when it wants to. I changed the thermostat. Didnt do the trick. Changed the thermostat temp sensor, no fix. Week later my 6 month old radiator starts leaking. Just installed new one and new cap and still same problem. Could I have bought a lemon thermostat? The truck does not overheat. Heater works fine, maybe a bad gauge? I dunno. I am lost any help would be appreciated.......Jerry

you can take the thermostat out of the truck and put it in boiling water. if it opens its good, if not, its not working.

if you have a one wire thermostat disconnect the wire and just ground it out, if the gauge goes all the way up it is good. If it is a two wire one disconnect the connector and jump the two wires, the gauge should go all the way up. if it does the the sensor is bad. if not you have a wiring issue

yes I changed the thermo sensor already. It has to be a wire issue. I have ran out of options. Thanks

I would say its either a bad gage or temp sensor. A T-stat will not fix that problem.