Clarify whether you're after an old HPP+ to set rudimentary parameters as speed limiter delete, wheel dia., change shift points, maybe 'perf.' or 'econ' timing. There's more elaborate and effective methods involving custom wiring adapters from the car to a laptop with related software for major alteration to the pcm. They also provide opportunity to destroy your motor if the program is incorrectly altered. Those two years you mention run different versions of OBD- and require different hardware/software if going after the latter approach. You can also order a "mail-order tune" of varying extent and quality from companies or individuals specializing in them.
I would highly recommend reading ALOT through the PCM Programming/Engine Management section of this forum to learn the various schemes, nomenclature, program names, sources, other's experience......
\'96SS SOB: SSRI, Herter Tune, Tri-Y II, , 3000 Edge, F/HO bars, METCO extendeds with CV MMC, Bilsteins, currently Vredestein Ultrac Sessanta (315/35 rear)
\'96FWB BUW-Butt Ugly White: PCMPerformance tune, HDFA w/ swissed filter, 1/2 SLP s.s. catback with H- and Flow Super 50s, oem opti rebuilt 3 times, SS Bars, METCO LCA, Airlift 1000, Monroe SS, PowerTrax No-Slip, CTS wheels with +1 rubber. Finally, wait for it... LT-4 knock module!