While i was driving my car was jerking back and forth while my rpm were dropping then jumping back up again. I’m not to sure what is going on.
Answer: Not sure what you mean by you replaced the “6th cylinder”. The RPM going up and down could be an engine misfire. It has a strange feeling like that. What codes do you have currently?
The other possibility is that the transmission is the cause. Depending on what speed this is happening, the TCC (Tourgue Converter Clutch) could be going on and off. The TCC almost feels like another gear between 3rd and forth (overdrive). If this is going on and off, basically this will cause the engine RPM to surge because the transmission shifting up and down.
The most common cause for this is the TCC solenoid inside the transmission, but it could still be and internal problem with one of the clutch packs. You need to see if one of the stored codes in the computer is related to TCC, usually a code like P0742. If it has that code, have a transmission mechanic diagnose the problem.