04 Silverado Shift problem

My new 04 Chevy Silverado 5.3L Auto trans shift poorley at low speeds. The 1/2 shift slips then engages. This only happens when taking off slow. At part, half and full throttle it shifs just fine. I suspect this to be a computer programming problem. My 1999 5.3L did not have this problem! Has anyone else experenced this problem?

My 03 does the same thing, from 1-2 while slowly accelerating it switches out of first... then a delay... then bumps into second late.

There is a TSB for a updating (new program) for the ECM, mine goes in this week..

-Bill