Called service manager this AM and he said it sounded like something with the clutch. It will be a few days before they can send their flatbed to pick up the sling.
Just spoke to the dealer service manager. He said he's pretty confident that my problem is the magnetic clutch switch some of you have mentioned. He added that this is a very common problem. Hopefully I'll have my Sling back in a couple of days.
To finalize this thread, I'm pleased to say the sling is shifting just fine since I picked it up from the dealer this AM. The magnetic switch was the culprit. Thanks to all who offered advice.