Has my thermostat gone out???

[saulgoode]

Hey guys!

Anyone want to take a shot at diagnosing an over heating issue.

2006 5.3 w/ 200,000 miles.

Regular running temp 210-220

Recently It has started to creep up to 225 then surge to close to red line (260) then the fans kick in and bring it back down to around 210.

This only happens in stop and go traffic or stop lights, and has been increasing in frequency.

I have been noticing this for a couple of weeks, but never get to full on over heating.

Today in heavy traffic it was doing this a lot 225 then surge to 260 then fans then back to 210. I was a little concerned so I kicked the heat on full, it would blow HOT for maybe 5min then nothing but cool air.

All signs point to thermostat in my opinion.

Any thoughts?