cooling system airlock

I just had a cooling system flush on my 1991 Bravada. I believe I have an airlock that I can't get out of the system.

The problem shows up in the operating temperature that fluxuates from 190 to all the way hot. I've checked the thermostat, rad, rad cap, and pump. I've tried parking it on an incline and running the engine with the cap off. The only way I can get it to cool off is to either remove the thermostat or put a hole in the thermostat flange. When I run it with a hole in the thermostat, it won't get over 125 degrees. I've almost ruled out a head gasket in that there are very few bubbles showing in the coolant and the oil doesn't get milky.

Any help with a diagnosis or with dealing with that possible airlock, will be appreciated.

The normal temperature varies from 190F to 210F.
Does your heater blow hot air after the motor warms up?

Thanks for the reply,
Just after the system flush, the heater did not blow warm air. But, eventually it began to work properly.
Since my last post I put in a 180 degree thermostat with a 1/8 hole in the flange and it drove at about 230-240 degrees. So I bored the hole to 11/64. That caused it to run at about 125-135 degrees with the outside air temp at about 50. This was up to 10 degrees hotter than the previously mentioned thermostat (195 degree with a 11/64 hole in the flange). (With the 195 thermo, the 11/64 hole was the smallest that would give me a temp that wouldn't go too high) So I placed cardboard in front of the rad and it runs at about 150 around town and about 180 on the interstate. For some reason it operated better with a 180 than a 195.
That's a rigged up way to get it to heat up closer to normal without it going too hot. Any further diagnoses or ideas about a long term fix would be appreciated.

Now I'm wondering if the flushed junk has shifted to your radiator. Can you feel the bottom of the radiator on the drivers side for heat?

Now I'm wondering if the flushed junk has shifted to your radiator. Can you feel the bottom of the radiator on the drivers side for heat?
Hi Chris,

The bottom of the radiator is hot on the driver's side but it is cooler than the upper area by the filler neck.

When I refilled the system after changing the thermostat, I ran water through the radiator. The water that came out was clean.

Your thoughts are appreciated.