I'm having my transmission looked at today, if there is a slip in 4th gear, do i need to replace it?

I recently bought a used 96' oldsmobile cutlass supreme. I took it to AutoZone because my check engine light was on. One of the codes is P1870. It says that transmission component slipping. Transmission is in 4th gear with TCC engaged and the ECM has detected excessive slippage when comparing the input shaft speed to the output shaft speed.
We checked the tranny fluid and it looks fine. the other two causes listed are "trailer towing may set code" which i don't know what that is, and the other says "internal transmission fault". Will this be the undoing of my car? I only paid 300 for it and don't want to have to buy a new transmission.