Clutch Sometimes Slipping in 4th and 5th gears!

Clutch is slipping.

2nd and 4th gear ratio codes. No matter the cause, the transmission has to be pulled. Low end at a garage is $1000, top end $2500+.

The problem is inside the box, could be a sliding sleeve and gear

sounds like if your talking about a manual most likely needs a clutch if your pedal is fully releasing

probably the gear is wearing pout

P0734=A/T 4th gear incorrect ratio. This has nothing to do with the speed sensor. If the speed sensor was faulty, it would also set OTHER gear incorrect ratio codes. My experience tells me the 4th gear incorrect ration indicates the torque converter clutch (TCC) is slipping and nothing more. Unless there was a speed sensor DTC (Diagnostic Trouble Code), the sensor is not the issue (yet). The fact P0734 was set (trust the computer), the TCC is slipping (out of range). Question: Maintenance history may indicate the wrong transmission fluid may have been introduced. Hyundai's Transmission fluid is strictly SPIII... there is no substitute. The incorrect fluid will cause 4th gear slippage. Now, having said that, it doesn't mean the 4th gear (lock-up) clutch isn't worn out. Have a qualified/certified Hyundai Service Technician properly diagnose this issue.

your clutch is more than a little worn out and needs replaced, it is slipping. in time the slipping will also be in the lower gears and any time a slight hill is encountered.

Hi:
The shift pattern is pretty much the same on all 5 speed cars. The top row is the odd numbers, 1-3-5
the bottom row is 2-4-Reverse. The center position is neutral

Here is the key: The shifter is slightly spring-loaded to the center position. If you hold in the clutch pedal and pull the shifter to neutral, and let go of it, it will automatically be lined up in the position, that if you pushed it forward , it would go to 3rd gear, and if you pulled it back, it would go into 4th gear.
This way, to start driving, you start out in neutral, grab the shifter lightly, and push it first to the left, then forward. This is first gear, where you start out. when you want to shift to second, push in the clutch, and keeping left pressure on the shifter, pull all the way back . Here is the easy part, 2nd to 3rd. When you are ready, push in the clutch, and just push the gear shift forward , till it hits neutral, and is spring loaded to the middle. Then you just push it straight forward to 3rd, then next shift, straight back to 4th.
Last gear, 5th: push forward to the neutral row, then Push to the right till it lines up ,and forward to the 5th gear. Reverse should only be shifted into from a dead stop. Find neutral, push the shifter all the way right, then pull back towards you. Hope this helps.
Practice a bunch in the driveway!

Since you did not say what type of transmission you have i will suspect the clutch is slipping if it's a manual.
If it's an automatic, it could be several things. Low fluid level...clogged filter, fluid needs to be changed..transmission serviced...weak pump, bands/clutch packs worn...etc
Good luck..i hope this helps, please rate me a fixya.

I don't know if I can help but as an owner of a Hyundai Elantra 2000 GLS with 205,000 miles and the original clutch and transmission I'll try and help!

I always start with the lowest cost solution first and avoid mechanics as much as possible!

Have you checked the trans fluid?
It should be changed every 30,000 miles!
Sometimes a Lucas Trans Fluid will cure - fix slippage!

Have you checked for a clutch adjustmet!
An adjustment can cure - fix slippage!

Are you a clutch rider with your foot always on the clutch?
If so you may have worn out the clutch!

How many miles to you have on your Hyundai Elantra 2000?