Recently (past few months) I noticed after my 35 minute commute to and from work that when I park and turn engine OFF I hear what sounds like gurgling/bubbling coming from radiator area. Car runs fine. No smoke and temp gauge normal.
Today I got stopped on highway due to wreck. I sat there in 2 degree weather for 20 minutes. After 20 minutes I began to smell coolant burning and then saw smoke coming from my right front wheel well (V6 Sebring 2.7L). I noticed the temperature gauge begin to climb to halfway mark... it wasn't registering HOT. I turned heat to high and it maintained at midway mark but continued to smoke (not horribly but enough to get my attention). Once traffic opened up and I began to drive the temp gauge needle dropped to barely above COLD but the smoking stopped.
I recently had the oil changed where they tested my coolant and said it was "really good"... it was flushed and filled this past spring). I haven't noticed any coolant leaks and never before smelled it burning and never any smoke. Just the persistent gurgling sound after driving. HELP!
Is it likely to be air in the system? I haven't checked the level because it was just done at last oil change and it was fine. I will check it today though. Could a thermostat cause this?

Could a thermostat cause this?
Yes, or more likely a partially clogged radiator.

Without checking it myself, I can only guide you on what could possibly cause this.

Low coolant from an air pocket
Bad radiator
Bad thermostat
A leak somewhere
Head gasket

Corrosion or phosphate scale has likely blocked off passages in the radiator. If you end up replacing the radiator, refill it with 50/50 mixture of G-05 antifreeze and distilled water. Read your Owner's Manual on how to drain and refill the cooling system, in order to prevent air pockets from forming. Also, have a leak down test performed, to ensure the head gasket has not blown.