95 temp gauge

Hey all
I am working on my friends 95 Geo tracker. She said it was overheating. I removed the radiator and it was junk. So I replaced the radiator, thermostat, radiator cap, and hoses. I have driven it for 3 days and it worked fine until today. Today the gauge started to go into the red again. Can't figure it out. Any ideas? :crying:

The temp gauge in my 96 was trash. It went to normal temp after 3 minutes of driving and never above normal. I bought a aftermarket gauge and pillar mount. I get good readings now.