Yeah... I had that issue on other cars before. Shifted smooth, no issues. Figured, "Meh, I'll just do an all over service" Then the tranny started shifting real hard, and eventually not shifting at all. Never had that problem except on my Caddies (the Cougar shifted much better afterwards) - one was at only 70k ('77 Sedan DeVille), and the other at 165k+ ('81 Eldorado). I've since stuck with the ''if it ain't broke'' addage.
Hopefully it is just the solenoid... best of luck!