When you put the plugs in, did you change the cap, rotor and ignition wires as well? If not, I would install those, and check the fuel filter and rubber hoses as well. If the timing belt has not been changed, its possible it has stretched and needs to be replaced.

There was an issue with the distributor pickup failing, but those usually just died whenever they felt like it, and sometimes would restart instantly, and sometimes would take hours before they would restart.

A stumble/hesitation sounds more like a wire/cap/timing issue, or a fuel flow issue. Those cars, with that motor, were pretty solid runners, and 100,000 miles is about time to replace original ordinary wear parts if they are still present or are of unknown condition. Gene