It could be the TPS. Todd4198 had a bad TPS, bought a new one, and replaced it. Upon replacing it, his idle would jump to 2000 RPM in park. It sounded pretty bad changing from park to reverse or drive. He exchanged the TPS for another TPS and the issue was resolved. Apparently, he replaced his bad TPS (rough idle and crappy shifting) for a defective one (high RPMs in park). I want to say it's roughly $30 for the part. Make sure you pull the throttle body to change it. If not, you'll risk stripping the Torx that holds it into the throttle body. Ask me how I know...
97 ZJ - 5.2/242, 4" lift, 31s, locked, armored
14 JKU Sport S - Stock