Hyundai: Hyundai Transmission, hyundai elantra, exact problem

Question
I have a 1995 Hyundai Elantra with 60,000 miles and an automatic transmission.  Recently and sporatically the transmission slips out of gear when the car is stopped.  It will then either clunk back into gear on its own or will require that I rev the engine a bit before going back into gear.  When the car is in this "neutral" position the gear shift can be moved into neutral and back into drive without re-engaging the transmission.  It seems to do this more often when the car is warm rather than cold.  Please make suggestions as to what might be causing this and what the remedy might be.  This is my daughters car and I would like to get mine back asap.  In advance, thanks for the help.

Answer
Hello, I know what it's like to want your car back :). I had the exact problem with my Elantra and I had to replace the transmisson sensor.  It's a piece right under the transmission, really simple for a mechanic or someone who knows what there doing to replace.  It cost only about $110. The sensor tells the transmisson how fast or slow the car is going so it can either down or up sift.  The transmission sensor is what I would check.  Have a good one and let me know if that helps.  It should.