Need help with sputtering/stalling truck

[Jobe72]

I have a 1972 GMC Sierra with the stock 350/350 and 3.73 gears.
The truck ran great when I got it back in March up until a month ago.
Truck already had a MSD HEI installed.

All I did when I got the truck was replace the carb with a Edelbrock 1406.

One day the truck just started sputtering under 1/2 to full throttle. No changes were made. So I checked the fuel filter and it was clean(has a pretty new tank). Took the carb off and cleaned it out really good (it was clean). Changed the fuel pump out (what a pain in the ass). Changed the plugs and wires. Checked the cap and rotor. It all looks good but the problem persists and makes the truck pretty much undriveable. Truck starts and idles fine, then get on the gas and it sputters along and sometimes stalls out until I back off on the throttle.

Any thoughts?