I have an update to my problem.
It turns out that the service guys OVERFILLED my fluid and that was causing the hard shifting. I called 1-800-NISSAN-1 and made an official inquiry and the dealer looked at it again, and together they were able to solve it.
The dealer drained the surplus fluid and now the shifting has returned to "normal".
I was really impressed with 1(800) NISSAN-1. They really came thru for me on this one. (then again, the problem was induced by the dealer, so they SHOULD have come thru for me.)