I have a 383 in my 70 Challenger, which just had a fresh rebuild by a reputable builder. Tranny is a 4 speed, carb is an Edelbrock 1406, used because I couldn't find the 4367 I needed at time of the rebuild. Cam is new, stock grind, vacuum advance is connected, stock everything, timing set at around 36 degree total (that sound right?)

Ever since the rebuild, the car has had a major hesitation/bogging when throttle is applied from any rpm. For example, setting in my garage, at any rpm from idle to 4000 if the throttle is depressed it hesitates. Badly. It's even worse when I'm driving it around- the car often dies or backfires. The car starts easily, idles nice, choke works as it should.

I have heard the 1406 has a reputation for an off-idle hesitation, but this occurs at any rpm, not just idle. I have tried using all holes on the accelerator pump rod (if that's what it's called), and it makes no difference at all.
Here's the kicker- I am only pulling 12" of vacuum. What are you guys pulling on stock 383's?
Oh, ignition is stock Mopar electronic. I have changed ecu units- no difference.

That vacuum reading is low for a relatively stock build. I would like to see closer to 18 or more. Try this: Disconnect the vacuum advance, & plug the hose. Install a good vacuum guage to a maniflod source (a source below the throttle plates)...Start engine and let it idle, slowly move the distributor until you achieve the highest steady vacuum reading. If you can't get much beyond your stated value of 12", then I would strongly suspect incorrect valve timing. If you can get a higher reading, then look at the guage and retard the timing 2 inches and lock down the distributor. Drive the car and see if the hesitation has been minimized. If that fixes it, then re-connect the vacuum advance to the ported (above throttle plate) source and drive it again. If it pings you may have to "tweak" your timing a bit or have your distributor advance curve evaluated. Sometimes the mechanical advance can interfere with the vacuum advance and cause pre-ignition...such as with incorrect springs, etc. If it still is acting up, you may have a carb issue, but I would see what kind of vacuum reading you can get first. A big vacuum leak would cause other driveability issues, and you said that it starts and idles fine...Let us know what happens!

I'm wondering if you dont have enough initial & that's making your vac that low. I have alot of probs w my 1406 also (elec choke), choke (full 12V) comes off WAY too fast and b 4 that the vac break (choke pulloff) is inop so it's skewed both ways. Went from from 95's to 98's on the pri jets as it was lean. Try this, find some way stiff springs & sub em in & take it for a run or even just gun it in your driveway & see if the hesitation goes away this'll put you on the power circuit all the time. Trying to pin it to either timing or lean or may b elsewhere (multi indexed crank gear on the rebuild installed on the retard key) just thinking out loud/brainstorming. This is an interesting case, holler what it ends up being. Do run it for 10 seconds (on level ground)then pull the top & the fuel level must b at the notch(s) in the fuel baffles on each side and assuming the AP has a GOOD stream when pulled