I can report the same experience with my '98 GT wagon. Took it in for the 30K checkup, and to complain about the worsening hesitation issues. They did the same thing as on yours, in addition to the comprehensive 30K checkover/maintenance, and installing a set of P7000 SuperSports.
What a difference! It actually feels better than I can recall it feeling even when new. Launch is much better, and everything is smoother and faster. It is funny how your car gradually deteriorates in performance, and you don't really notice it until you take it in for a good servicing.