Somebody makes the combustion chamber cleaner for Mopar, so I would suspect that Wynns, Chevron, etc. have the same product available at a parts store or service station.

If a PCM update was performed, there will be a grey sticker near the emissions label, and also a small white one on the PCM itself, showing the revision number (if the tech followed the instructions)

'96 was the first year for OBD-2 on Jeeps.