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.
-RaceJeep: 1998 Deep Slate 5.9, AC delete, Roof Rack delete, Accel cap, rebuilt 249, Accel rotor, Champion copper cores, 14"x2" air cleaner, 52mm TB, Mopar M1 4bbl, catch can, Bilstein 4600s. Lots more in the works...