On the way home from work I noticed that on the 2 - 3 shift the 4T45E auto trans slipped slightly each time before settling into 3rd gear. This is on light easy acceleration. I didn't get on it to experiment further. Hope its just a fluke. 1 - 2 and 3 - 4 shift felt okay, felt as normal.

 

I posted a similar post long ago. Did it suddenly change or has it been doing this all along. What someone told me was that this transmission has a constantly variable lockup clutch on the torque converter. On light to medium acceleration it will do a "soft" lockup of the converter immediately following the 2-3 shift and it sounds like a slip. Try selecting "I" and see if the 2-3 change is crisper. 20,000 miles later mine still does this. Interestingly, When I have a few hundred pounds in my utility trailer the programming responds to the load and it does not do this.
Hope its nothing serious in your case......Good Luck