Start at the basics,check all wires for to high resistance,cap and rotor for corrosion,If you have not done a major tune up,do it now,this way you have eliminated a major group of problems.After all of this and you still have the problem, I would lean to wards the position sensor. but before you go into that do a fuel pressure test. If you have good fire and good pressure the next would be that pesky position sensor.JNT