If you still suspect a vacuum leak, take some carb cleaner and spray it around the lines. If the engine stalls, or drops in RPM, you've found the leak. Silly question, but is the IAC plugged in all the way? I neglected to push the connector on all the way (I was in a hurry) after I cleaned my IAC and it idled high in neutral and park, but drove normally.
March 2014 GCOTM. 1998 Deep Slate 5.9
On the Jeep:Hot intake, 52mm TB, Summit 8mm wires, catch can, 703s, insulated fuel rails, indexed Champions, Bilstein 4600s, Ironman mounts, Lotek 2GP, lots of gauges, sparkly paint.
In the garage: M1 4bbl Eibach lowering springs
In the works: Addco/Hellwig sway bars, nitrous, full polly bushings, full exhaust, data logging, billet UD pulleys