Misfire, with this many miles, when was the last time the wires got changed? I had an 88 Dakota that would develop a miss every other time I changed the sparkplugs and had to change the wires to fix the problem (like four times in its life I owned it), carbon core non-solid wires are not designed to maintain continuity more than a couple times of disconnecting cap or sparkplug connections.
Agree the rotor may not have been seated all the way down, but as a check, pull the rotor on the shaft in an upward direction and see how much it can be raised, check the rise by twisting, see if the rotor is riding up on the cam helical gear, if it does, the housing on the bottom of the distributor could be worn down from scraping can add slop and then start destroying the cap and/or rotor.