Transmission Issue

[09z71]

I have a 2009 5.3 V8 silverado... practically brand new only 6k miles on it. Recently it has been doing something weird when putting the truck into reverse. Sometimes it acts like its hung between reverse and neutral. The dash shows that the truck is in reverse, but when I give it gas it the rpms go up but the truck doesnt move. Still under warranty, any ideas what would be causing this.

I have also had it in the shop 3 times previously because the driver window randomly quits working it is on its second regulator, has had the door switch replaced and a new window motor put in. any ideas on what would be causing this problem.

 

Thanks David