Original carb? Very first thing to check is the throttle shaft coming out of the carb base on the driver side. They tend to wear there causing a vacuum leak and poor drivability. Disconnect the gas pedal and any spring(s) then check for play, if there is any it's going to have to be drilled out and bushed. There are kits you can buy with the drill bit and bushings. I personally have used QP and Cliff's kits with good results.
Quadrajet Power, Jet Chips, Mikes Carburetor Parts and Cliff's High Performance all promise USA made ethanol proof parts in their kits. Stay away from basic no name and auto parts store brand kits full of low quality off shore made parts. You'll pay more for the good stuff but you get what you pay for.