Running, idling, not driving

[Squadron]

So I've got my '47 ford (v8 flathead) starting and idling. It will warm up and then I push in the choke and it hums pretty well.

However when I put it into gear (forward or reverse) it craps the bed. Jerking, popping, barely creating enough power to move the car forward.

It doesn't matter how gently I give it gas (if I go a hair too hard it dies).

I got the carb completely tuned and rebuilt about a year ago and it's a 12v system with new plugs. I've made sure the fuel pump is pumping (it still has the mechanical pump).

What should I be checking? Some sort of vacuum somewhere?

Things that have changed since the last time I had the car running under load (it was running very rich but not dying):

* Had the carb tuned and rebuilt off engine
* Put the new carb on
* Hooked up and primed the carb with the fuel pump
* Replaced the ignition coil

tl;dr: Idles smooth, but as soon as it's asked to do work (in gear) it complains bitterly and tries to die.