Troubleshooting stumble at idle in gear

Ok it sounds like a "misfire " at idle then? Can you get someone to sit in the car with it in gear and you hook up a inductive timing light to all the plug wires one at a time ? point the timing light at the valve cover or inner fender, you'll see the light being erratic on the suspect cylinder. Then you'll have the misfire pinpointed, if it is across all cylinders, then it is in the primary side, the points (or Ignition box if electronic) or in the distributor cap or coil. it could be a bad wire, I know they may be new doesn't mean they aren't bad. Parts these day are hit or miss. also sometimes the boot end isnt clicked all they way onto the plug or all they way down in the dist cap etc.