Hesitation in acceleration and high rpm "cough"

[Longhorn Al]

My truck has had a hesitation when I press the gas pedal off idle. It sort of almost stalls, then catches and goes. We advanced the timing awhile back and it went away. But now it's back. I've talked to some guys and they can't think of what it could be. It did it before and now after I had the heads replaced. And I have an electronic ignition.

Also, I've always had a problem with what seems to be a high rpm cough. Off the line, it'll squeal the tires for quite a ways, then you can hear it really get into it. When I reach about 55 or 60, the engine coughs pretty hard. The whole truck will sort of rock. It's like it's not getting fuel, but we're not exactly sure. I've got the original 4 barrel carb on it. Is it most likely something wrong with that?

Thanks for any help. These are extremely annoying problems.