my 99 elantra is now moving only when the Over-Drive switch is turned off. When it is turned on, the engine just revs up...seems it is slipping to neutral while in the top-gear.

mechanic informed that I need to replace the transmission.
any better cost-effective solutions?? seems it not worth to spend 1500-2000 dollars for an old car.

also, is there any problem if I run with Over-Drive switch off (then it is in 3rd gear) on road marked < 45mph (not on highways). Or will it die completely soon? It has 85K miles only.

 

The solution of this problem is replace the valves inside the trasmission and the sensors. If you done the repair the total cost is 600 including all parts.