Transmission Slip?

I own a 2001 Hyundai Accent. Not my first choice but it takes me to work and back (commute 1 hr. each way) Recently started noticing that it will start shifting back and forth from overdrive to fourth gear after I hit the 60mph mark but it will only do it after the car has been running for about 10 min. Fluids seem to be ok. Just afraid I might have to come up with a large sum to replace the tranny while I still owe on this car. Has happened before.

Car specs. 2001 Hyundai Accent, GL, Automatic, 62,000 miles, all service done properly and on time as far as I know. Bought 1 1/2 years ago when the car had 27,000.

Any ideas or suggestions will be appreciated.

I am guessing that you do not have the warrenty?

Are you using Dexron or Hyundai fluid?

No, the car no longer has the warranty. I bought it used at a hyundai dealership so it only covered to 50,000 miles.

I'm using Dexron.

First thing to do, get rid of the Dextron, and put in Hyundai ATF. Mitsubishi and Kia use the same fluid as well. You are lucky the car is moving after putting Dextron in it. I have had several people come into my dealership and they need transmissions. A couple of times the car was running fine, until they put Dextron in, and it didn't even make it out of the driveway. That would be my first step. If there is a check engine light on, it could be a throttle position sensor or pulse generators. Either way, start with changing to the correct fluid because you are definately decreasing the lifespan of the transmission with the Dextron.

wow i did not realize that the transmission fluid is that important. Whats the benifit of using synthetic oil vs. regular?

Who put in the Dextron? A Hyundai service center?