Just a lag? Or rapid cycling, - can't tell from your description. Even where you are I'm sure you've discounted the temp just being set close or higher than outside.
Set it on 60/MAX and observe any more consistent operation.
Did this autopart stores refrigerant refill at least have the moveable fill range pressure indicator according to outside temperature?
And if an original clutch, then indeed at 20 years old it may be letting go. Mine exploded 4 weeks ago on the interstate. I noticed just before that it was not blowing quite so frigid. Lucky me - there's still positive pressure in the system though.
\'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). Finally, wait for it... LT-4 knock module!
\'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, yes again... LT-4 knock module!