Auto Transmission Shifting Issue Since 4bbl Upgrade
The kick-down linkage probably needs adjustment.
Give it a couple turns (either way) and test drive
If the problem gets worse go the other way
Hard shift to late shift
Are the two issues you may get if not adjusted correctly
I just can't recall which direction corrects which issue.
I could quote the factory procedure but you probably do not have the linkage setup as the system has been modified.
It is quite possible it can't be adjusted as the 2-bbl linkage is different and the alignment may be off and causing problems of its own.
Alan