Wow, the tranny in my dads 2006 gmc slipped a few months ago, scared the piss outta me. I was driving felt it slip a little, then 1 min down the road nothing but rpm's. I pulled over, shut the truck off and started it back up and it wouldn't drive, put it in reverse and it worked. Then put it in drive and it was fine. We told the garage while it was still under warranty, but it hasn't done it since.
Hope you get your tranny fixed, wish you lived closer this way I could get you the hook up on a rebuild. I know a guy who builds, and rebuilds trannys for drag cars and everyday drivers. My bro got a Chrysler 3 speed tranny for $50 off of him, completely rebuilt. This guy knows his shit too.