Hyundai Repair: Overdrive shifts in then pops out of gear, hyundai accent, output speeds

Question
I have an automatic 1998 Hyundai Accent that shifts fine through the first three gears.  Then pops out of fourth, acting like the car was in neutral.  The dealership tells me that the fourth gear is gone and I need to replace or rebuild the tranny.  Other sources say it could be the end clutch causing the problem.  Is there a code for the end clutch failure or is it just a code stating the the fourth gear is slipping?

Answer
The other sources are correct that it's possible that it's an end clutch issue.  Unfortunately, there's often little way to tell conclusively and inexpensively without replacing the end clutch and seeing if the problem is solved.  You can remove the end cover of the transmission and remove the end clutch and inspect it, but the inspection may be inconclusive.

The transmission computer has no way of knowing the cause of slipping in fourth gear.  It simply compares the input and output speeds and determines whether they're appropriate for the particular gear.  In your case it could set a P0734 to indicate that the expected ratio isn't seen (slipping fourth gear).