What's happening is that the engine is defueling and allowing the shift to complete when cold. Mine has always done it. This is done because the trans fluid is cold which will cause the clutches to slip until enough fluid gets to the piston that locks the 2nd clutches. I had a 95 w/4L80E that didn't have this feature and I could feel it slipping on the first shift in the morning. It is a good thing.
02 GMC 2500HD D/A EC LB SLT
FLAME RED! Charcoal Leather Buckets
Pacer 16x8.5 Chrome Split Rims W/285R16 Goodyear MT/R'
Weston Nerf Bars
Fold-A-Cover
Lund Bug Deflector
Air lift Air Springs
Gabriel HiJacker Air Shocks-all 4
JUICED
Elkhorn 11X slide-in
Rinker 212 Captiva