Pop off that distributor cap and look real good with a flashlight all around the ignition module. Look for oil......if you see oil crankcase pressure is pushing oil up into the distributor. What that then does is covers the thin cellophane cover over the magnets on the magnet ring and on top of the module.
It will cause just those symptoms intermittent stall, as the oil film interferes with the Hall effect magnet trigger. If it is oil you can plug 4 of the five bottom holes in the dist shaft with RTV or drill some holes to relieve that problem. Then you can correct your PCV Breather system as a bad one causes this pressure.
If not oil check the grounds on the module for loose screws to the dist body, they are very sensitive to grounds. Tighten up and clean up all grounds, even battery to engine and engine to frame. You can test the ground on the module with a direct test wire to negative battery terminal, should have very low resistance.
Use an ohm meter on 200 scale, pos of meter to module plate, negotiations meter to neg battery terminal POST, not clamp. Should be less than .2 ohms, if more find the bad or weak ground.
If that is OK recheck gap on module to magnetic ring or lobes depending which model you have. The modules are very sensitive to that gap should be 10 thousands to 60 thousands....usually 20 to 30 is normal. If it gets loose or out of wahack will only Fire sometimes, giving an intermittent problem.
If that is ok verify your ignition wire provides a full 12 volts to the coil and make sure it is not coming thru a ballast wire that drops the module down to 9 volts which is what points need so they donít burn up. These modules can work on reduced voltage but perform best at full 12 volts.
It is an easy fix with a relay and very reliable if you have reduced voltage from a ballast wire. There are a few ways to fix it
Those are 4 things I would check, if those are all ok could be a weak coil, check with ohmeter and could be fuel pressure as well....
You just have to do some tests