We have a 66 Charger, ramped up 440. Auto trans. I had a problem a few months ago with the car running for about 10 minutes, then would shut down completly. Let it rest for 5 minutes, then it would start right up again. Finally it started doing it all the time, and would only run for about 10 seconds,then died.. Towed it to the shop, and they seemed to fix the problem. Now the car runs badly, and backfires quite a bit. I messed with the timing on the highway, and got it home, but cant get rid of the backfire. Does ok under a heavy foot, but when I let off, it sputters pretty bad. Do you think I just need to get the timing "Right on " and it will be fine, or do you think something else is up? Put new coil in,ECU,plugs.Electronic Ign. Choke is fine.Thanx. scott

My sight unseen vote (ECU)

years ago, I had a problem with a 401 jeep that go down the road a few miles, then shut down. cool it off and it would go again. tried a new coil...didn't fix it. changed coil wire...walla!! don't know what the boys did, but sounds like they may have fixed an initial problem. make sure your choke plate is opening up. maybe it's flooding out.

Timing chain slipped?

First I'd put a new ballast resistor on it.
Then is it a new distributor?? Check the reluctor to pickup gap say .008 But I like .004 and while your in there check for excessive play in the upper bushing in the distributor.
I've had some ECU's that really liked a narrow gap.
the vacuum advance should be unhooked and plugged at the carb till you get it running right (or forever LOL!)
Check your voltage on the in and out side of the ballast should have over 12 in.
Is you amp gauge toast?? Run a jumper wire across the posts to eliminate that as a suspect
What carb??

Go back to square one including checking the firing order. Check you bill see what they did. Check your distributor cap inside and out real good