96 SL2 transmission help

Get a scan done to check for trouble codes.
Ensure the fluid level is correct.
The 4th revving up could mean a pressure drop or certain solenoid is not working correctly. The scan might help on this.

For drive cycles, the computer needs to relearn after the battery is disconnected and a certain drive distance and time frame is required for it to be accurate. Try a 20 minutes drive on the highway and get back to city driving for a few minutes and then back on the highway for a few minutes and the dirve cycle should most probably be complete.

Just to add to this one is the only problem your having is when it wont stay in 4th gear?So did they put in a used transmission?See if it has any codes like khlow2008 said you can go to a auto parts store like auto zone and they will read the codes for free. Post the exact code numbers. Heres the scarey part when people replace the transmissions the wrong transmission will bolt right up and they have different gear ratios and will cause no gear codes and loss of gears will into the gear but drop right out because the computer think that gear is slipping. Heres what I want from you go in your trunk lift up your carpet on the right side of your spare tire cover you will see a sticker with all your rpo codes on it. You will see a mp6 or a mp7 on there tell which of those you have?Next under your hood by where your coil packs mount to left of that right where the transmission meets the engine is where your engine vin and transmission vin are. Give me the full vin on the transmission and The 8Th digit of the engine and the last 8 of the engine vin. That way I can see what you have to see if we have a wrong transmission installed etc.