08 Silverado Overheating!! Help!

[Rubicon500]

Last week, i ran into a store to pick something up and i left my truck running as my wife was sitting in it... came back and noticed that the engine temp was higher than normal!!

 

Once i started driving, it returned back to normal operating temperature. Since then, i have been keeping an eye on my temperature gauage. My observations have been that while driving the temperature is reading as it should, idling at a stop light for a couple minutes are fine, but when it's idling for 5-10 mins it starts to get hot. This problem has NOT resulted in a check engine light.

 

I have an 08 silverado with the 4.8L, and 130,000kms

 

I have never cleaned the throttle body on my truck, so i'm going to do that tonight.. as my idle bounces around quite a bit.

 

Could the thermostat require replacement?

 

Any help with other things to check to narrow down the problem would be much appreciated!!

 

Thx!