It is not burning the fluid, but rather it is mixing the two kinds of fluids that will cause the most damage.
If trans fluid is really being lost there are only 2 places it can go; past a seal or gasket or by mixing with the engine coolant. With either case it should be apparent.
Just some food for thought. You state that you have someone check and add fluid when you get gasoline. Does this mean a real mechanic on duty at a gas station or a pump jockey who is doing things in between gassing up cars?
Have you seen them actually put trans fluid into the transmission or are you taking their word for it?
Just posing a scenario in case the people who are doing this have no idea and choose to cover lack of knowledge by claiming to have done something.
I think they were entertaining your concern by checking and adding small amounts of fluid that may not have been necessary. If you are having the fluid level checked after traveling only a short distance the fluid level is more related to the weather, lower as the weather is getting colder. The fluid level can change by more than two inches due to thermal expansion. This is why the fluid level should be checked at a specific temperature range, 158-176 degrees F for this vehicle.
Check the fluid level after a 30 minute drive.