Hyundai Repair: 2000 hyndai Elantra, hyndai elantra, speed sensors

Question
My 2000 Elantra is jumping in and out of over drive, I took it to a transmission shop they said there was nothing wrong with the transmission but replaced the high speed clutches and the high and low speed sensors,We replace the power train control module and the main computer and it is still jumping in and out of over drive.Theis reading two codes P0734 and P1624 Can you help? Thank Debra

Answer
P0734 means the transmission computer detects that the transmission is slipping in fourth gear.  This could be caused by a faulty end clutch or faulty pulse generators, but you seem to indicate that these repairs have already been made.  Chances are you'll need to overhaul or replace your transmission.  

The fact that the transmission shop addressed the less expensive items first indicates they're probably an honest shop.  I'd recommend going back to them to see if they'll recheck your car for free and apply what you've spent with them toward the repairs you're going to need.  Most reputable places would do that.