I have a 2004 2500HD w/ lly and allison tranny (42,500 mi). Drove it to work last week and went to back into my parking spot and it would just reved like it was in neutral. Code on the column said "range shift inhibited". Got back into it at the end of the day and it was fine. Brought it to the dealer and it cost me $200 for them to tell me they don't know what caused it and to bring it back if it does it again??? From other threads, it sounds like it could be the NSBU switch. Any other suggestions!!!

What did they do for $200 bucks? Sounds like a NSBU to me

They checked the fluids and codes but still couldn't come up with anything. One of the mechanics even took it home overnight to test it out some more. Other than that, they didn't do very much. I wish I knew about this forum before and not after. Oh well, live and learn!