I have a 72 GMC pickup truck with a small block 350ci engine and a edelbrock 1406 carb.the problem I am having is,when the truck is in park at idle I can step on the gas and there is no problems,but when its in any gear and I step on the gas it wants to stall, I've checked for any vacuum leaks found none,I thought it might be the vacuum modulator on the transmission so I replaced it,but did not fix the problem.I heard it also could be the ign timing was off is that true.so if anyone can help me with the answer to my problem please do.

THANKS TO ALL WHO ANSWER

Does this have a pick-up coil inside the distributor?
The wire that connects the pick-up coil to the ignition module may have gotten broken.
Remove the distributor cap and look for one or both wires to be broken.