Transmission slip from 3rd to 4th shift

[temmert1]

I have a 2010 sierra CC 6.2l with 21k. This past week I have noticed a slight slip in the tranny when it shifts from 3rd to 4th. This is only happening in the mornings. My truck is garaged but it still is only 45 degrees or so in the garage. It does not slip during any other shifts and only in am during initial acceleration when cold, then it is fine. I do have a BB tune also. I have not had a chance to check tranny fluid yet but will tomorrow. Anyone else have this issue or have any ideas for me?

[rdnkcpa]

_{Since your truck is covered by the factory warranty why don't you let them sort it out? Having the BB tune in there under warranty may cause some issues, but the dealer can most likely diagnose a transmission slip a lot better than the interwebs.}