Toyota Repair: automatic transmission, powertrain warranty, transmission problem

Question
Lately my car has been jerking when upshifting while driving. Sometimes it will get stuck in first or second gear. I just got the transmission fluid changed about two weeks ago. What could be wrong with it? Its only a 2001 model, the car should still be in good shape.

Answer
You forgot to tell me what model the car is and how many miles are on it,you may not be aware that(if it's a toyota)the powertrain warranty is in effect for 5yrs/60,000 miles, so unless you somehow managed to drive more than 60,000 miles in three years I suggest you take it to the dealer and have them check it, if there is a transmission problem you could get it repaired at no cost to you.