Further testing(going to school/work for 2 weeks) shows that unless its a long trip 100+ miles, the airtab have next to no effect on FE. They have increased my stability in windy situations, so I'm going to leave them on.
On the flip side though an increase in milage over a long trip could just be due to highway gas milage, thus making airtabs useless.
I think the problem is that your energy use is more a function of the engine efficiency and not the drag caused by the aero of the vehicle. If more of your energy usage was from poor aero drag then reducing the aero drag would have increased your FE. I may just have to get some and try them on my xB.