99 Tiburon Transmission Problem

Im constantly having difficulties with the transmission on my 1999 Tiburon.
Over the past year and a half, I have brought my car to the dealer 4
times, with basicaly the same issue. My car "pops" into gear, and will
sometimes go into its "safe mode" and will just get stuck in 3rd gear. It
wont upshift or downshift. So the first time I brought it in, the dealer
just replaced my whole transmission, but that didnt solve the problem. So
then, there was a sensor that had to be replaced. That worked for a little
bit, but then the same problem happened again. The 3rd time it was a
pressure valve and the forth time I brought it in, a bad sensor. So it has
been running fine now for about 5 months..but , the problem is happening
again. Is there an issue with these tranmission sensors? With the whole
transmission itself? How can I get this fixed once and for all?

This isn't Hyundai's most reliable transmission, but it isn't their worst,
either. To put things in perspective, I wouldn't expect to get more than
100k miles out of the trans without needing significant overhaul work or
replacement.

There have been some issues with the pulse generators (input and output
speed sensors) and with the connector where they attach to the harness.
If that's the case, you will typically get either trouble code P0717 or
P0722.

There are actually several very informative technical service bulletins on
your vehicle which describe symptoms, trouble codes, and solutions. I'd
recommend going to www.hmaservice.com and browsing through the
transmission tsb's for your vehicle.

At this point, without knowing what exactly was found in each instance,
it's difficult to determine whether you've simply had a series of
unrelated problems or the dealer hasn't been fixing it properly. I'd lean
to the side that it was fixed properly at least on the last visit if it had
been operating normally for five months.