I just put in a new stock replacement electronic distributor on my 383 in my 70 dodge truck that already had electronic ignition. The shaft was very sloppy on the old unit and was causing it to ping under load no matter what I would set it at timing wise. I put in the new unit, timed it in. It idles great, and runs great at higher RPM's. The thing is at above idle and cruise RPM, it backfires through the carb, and makes popping noises out of the exhaust. It bucks and pops, but does not die, like it is breaking up somehow in the mid RPM range. I only changed the distributor, so this is the only variable. Any advice? thanks!

did you check the gap? should be .008

Mikee is right. Use a BRASS feeler guage too.

Does it have an adjustable vacuum advance? If it's bucking at cruise, sounds like too much vacuum advance. That's what mine does if I dial in too much.

Double check the plug wire firing order. It's easy to get two swapped.

The pickups in the new MP distributors are crap. Swap out the pick up with your old one.

X2: pickup gap/bad pickup/too much vac adv. I guess too much vac adv timing and or rotor phasing. I'd unplug/cap the vac adv hose (easy check) & see if that makes it better/worse/no change & vac adv also alters rotor phasing

Check for timing chain slop too.

I'm running MP distrib and I was amazed how off the gap was in the thing. check that 1st.

Ok I checked the gap, and it was .008 as it should be. It did turn out that the vacuum advance was way off, had to turn it clockwise with an allen wrench about 8 turns to get it to where it liked it. Runs great now. Thanks for all the help guys!