Transmission slipped, causes?

[IIv SHaDoW vII]

I was pulling into my school parking lot the other day and my transmission seemed to slip out of gear around the corner then popped back into gear a second or 2 later. It was really hot that day (over 100 degrees outside) and I didn't check the fluid that day because I would have been late to class. When I checked the fluid today (70-75 degrees outside) after driving for 10 mins and while in neutral, the level is just a little over the full mark (overfilled about an 1/8 inch). The fluid looks ok and the transmission has always shifted fine with NO slipping or noises. The problem has not reoccurred since (3 days of driving).

Could the fluid just have been expanded way too much that day and caused the tranny to slip because of the 100+ degree weather?
I dont have the best of tires on my car, could it have been a loss of traction thing?

I know I am assuming the best, but I just want to know some opinions here.. I cant afford a tranny rebuild right now.

 

[stayflalfy]

We dont have tranny coolers in our cars so the heat could have caused the fluid to expand and slip. If this has only happened this one time i wouldn't worry about it until it is a consistent problem