FORGET THE AIR BUBBLES - THAT AIN'T IT! Think about what you wrote "Last night she ran fine all the way home (for about a 45 min commute in light traffic) " There ain't no way in that hot spot down below that would allow an air pocket to sit there not cooling for 45 minutes then BOOM cause the car to overheat. If it was an air pocket - it would act up as soon as you hit operating temperature. I would suspect three things in the following order based on the facts you give that as soon as you came off the freeway and arrived at home the thing overheats.
1) Since it runs fine on the highway where there is a lot of air going through the rad to cool it - I still suspect the viscous fan - if it does not draw enough air through the rad - you will have the problem you see. If the problem is intermittent - so could the fan be intermittently acting up - getting ready for total failure.
2) if the thermostat was sticking it should be acting up from cold going to warm as it tries to open - to have the car run for 45 minutes with normal temp then overheat - then when you cool the engine it acts normal for awhile makes me doubt that it is the thermostat - but what the hay - cheap to try. I would still run the car for a couple of days without a thermostat and see if it still overheats - if it does - go back to suggestion #1
3) Since you say the aux fans do work the only other thing that I can think of is a head gasket -
ARE YOU REALLY SURE THE VISCOUS FAN IS LOCKING WHEN THE ENGINE IS HOT???? If the fan is not locking when the engine is hot - the car will work good when you have enough airflow from faster speeds - but will climb in temp. when you go slower if the viscous fan does not pull enough air past the rad.
Since I cannot see you car - I am using the same common sense logic I use when I diagnose my cars. Hope you can see my logic.