Hyundai Repair: 98 elantra slipping out of gear when switching to 3, hyundai elantra, diagnostic fee

Question
I have a 98 hyundai elantra which slipps out of gear.  When I accelerate, between either 2nd and 3rd or 3rd and 4th it slipps and revs up.  When i let off the gas it revs back down and switches into gear than its fine until i stop and start again. The transmission was flushed and filter changed. I brought it to a transmission shop and they couldnt find the problem and said it may be a seal.  Any advise on what it could be and how to fix would be appreciated.

Answer
Most likely, it's an internal transmission issue requiring an overhaul or replacement.  If you're willing to invest in a diagnostic fee (usually about 1 hour labor) I'd recommend taking it to your local dealer for diagnosis.  My experience with transmission repair facilities (especially chains) is poor.  They tend to want to do an overhaul or replacement no matter what the problem is.  I'm especially leary of the one you went to because they don't seem to know what's necessary to fix the issue.