Didn't you and I have a phone conversation about a year ago and you were having simular probs (was it a head problem at the time) ??

I 'd test your fan clutch . You should hear it "roar" into action as soon as your engine is getting a little over heated . Same sound as in the first thing in the morning when your warmup idle is initially high and it takes maybe 30 secs to for the fan to loosen up . They usually last a little longer than 3 years but you never know.

Also , when I 'm toubleshooting a cooling system , I'll take the radiator cap off , take out coolant till there's only about 1/2 " of coolant over the tubes , start the motor and bring it up to temp with a themometer stuck in the fill neck so I can keep an eye on things. If your thermostat is working correctly , you should see intermitant coolant circulation as the temp reaches normal running conditions.

If you have a head problem , which can cause overheating and is very common, you may see "belching" of the coolant . You can also have the radiator tested for presence of CO

Be careful