I like NGK and with either them or Champion I have had no issues. You could OHM each plug wire. Most likely it is just one hole not firing 100%. Lots of cheap wires on the market. Seeing the distributor was replaced there are a couple things you should check. One make sure all the wires are seated correctly. And secondly ask the shop how they set the distributor. The distributor needs to have the sync signal set. If it is not set correctly it can cause some erratic running.