I put in a new AC thermostat and I think I may have air in the system as the temp goes up and down from 190 to 205 when driving normally. What I mean is the temp goes up and down in a pattern like a sticky stat. I thought the new one was a bad stat so I got another one from the dealer and still the same thing. I have tried opening the bleeder but only coolant comes out. Is there a proper procedure to do this? Also around the same time I put in my maxitork chip. Could this be causing any of these issues? My egts are fine. I also think I have heard coolant sloshing thru the heater core sometmes so probanly have air in it. The weird thing is when I put in the stat originally I drove it 1300 miles on a MI trip and it worked fine but when I put in the chip it seemed to start. There are no air bublles in the overflow while running, no coolant loss and the hose does not get hard when cold. Everything seems fine but the temp gauge swinging up and down is driving me crazy.

I have the exact same problem. Tried cleaning the radiator and changed to an AC Delco stat. Temps came way down, but now they fluctuate all the time. Never did this before.

I have/had the same. I have always kept my rad and cooling system clean. Last T stat I had, the temp sat steady at 195. When it failed and I replaced it last spring (with new AC) the temp would go to 195 then drop to 180...then back up to 195. After about 2 weeks it settled down ad sits about 185. Not sure if it is common to the AC stats or maybe the year of our trucks (mine is a 1995).

When I replaced mine with the AC/GM part (maybe 3 years ago), it would go to about 195 when first started, then drop to about 180-185 and stay there until shut down.That lasted several months, now it just goes to the 180 area and stays there all the time.

Check the wire for the sensor in the drivers side head. Mine was makin' my gauge go crazy. I've changed the sensor since then also. I posted the part numbers for both coolant sensors in the part point sticky.

I was having the same problem, temp changing and sloshing in the heater core, I back flushed my header core, you wouldn't believe what came out out....anyway that stopped my problems.

A +1 on back-flushing the heater core, did that when i flushed my whole system and couldn't believe what came out. All kinds of junk and some stuff that looked like dex-cool Jello. I'll never use Dex-cool again after seeing that.
Don