I had something similar (I had to tap the gas lightly on 1-2 and 2-3 shifts). Cleaned the MAF and the problem almost went away. My theory is that when I let off the gas the RPM fell too fast due some MAF/IAC issue.
Also had very rough idle for the same issue, much better now.
One more related issue, drive at a steady 25-30mph in 2nd in slight downhill and quickly take your foot off the gas. It used to buck for me (same reason).
Tiv
