When you measure the ballast resistances, first connect your ohmmeter leads directly together several times and take readings of just the ohmmeter leads themselves. Average those readings and then subtract that from the readings of the ballast resistance.
Ballast resistances are to be measured when cold. 5 ohms for the high side is OK; 1.9 ohms for the low side in not OK. It should be around 0.6 ohms cold. It will increase to 1.5-2 ohms when fully hot, which takes about 1 minute of running.
A high value on the low resistance side of the ballast will reduce spark energy as Mattax says, and that could cause irregular operation. And if the spark plug wires get high resistance or even if the spark plugs get a high resistance inside, that will reduce spark energy.
An erratic ground on the ignition module body can cause irregular spark, and the reluctor gap like mentioned by halifaxhops has to be steady. It could be a bent shaft or a worn distributor shaft bushing.
Finally, if the leads from the reluctor to the ignition module are reversed, then the timing can be jumping around, and you might have misfires.
