99 Pontiac Firebird over heatting?

[RCompService.webs.com]

It just recently started. It has never heated up this fast before.
It heats up to about the middle, which is normal after about 15 minutes of driving. (210F) Then it gradually goes up while driving.. and seems to go jump back and forth. Going back to the middle when I make a stop.

Could this be a sensor malfunction? I havn't noticed any leaks and have not done anything normal. I live in Texas, the weather has been it's hottest is years, I'm sure that doesn't help.

Any ideas??? Thanks!

 

[melsg5]

if you can get your hands on a infared heat sensor gun to measure the actual temperature you can determine if it's a false reading, otherwise it could be a bad thermostat