92 1/2 ton 4.3 liter won't idle cuts out

I have replaced the distributor, TPS, O2 sensor, fuel filter, Air idle sensor, plugs and the ECM but it will not idle once it is warm and the
engine cuts out when driving down the road. It's not a miss, it actually
cuts out. Could it be the coil? I don't think so but it's a stab in the dark. The tach jumps up and down like there is a short. Have not found one.

I replaced everything you did in my 91 4.3 and it was running flawlessly and then one day it did not start at all, it didn't cut out while driving, I got lucky and it was in my driveway but it would not start. It was the pick-up coil (not the ignition coil). It may not be the same thing, but it may be a place to start.

where did you get the dist thats one of the main rpblems with 4.3 5.0 and 5.7 back in the early 90s changed em to plastic newer version and not so bad