1972 c20 running problems

[thetucks]

I have a 1972 c20 that I picked up last week. it was setting in a barn for the past 7 years of its life. I had to replace the fuel tanks with a salvage yard swap and a new battery. she started up and idled fine, but when you push the accelerator it cut out and died. come to find out it was only firing on 4 cylinders. I replaced the spark plugs and tried it again. still only 4 cylinders. then I went back to the salvage yard and got an hei distributor and put it in. now it was running on all 8, but still cut out and died when pushing on the gas. so I bought a carb rebuild kit and rebuilt the carb. put it back on and it did the exact same thing. I eded up rebuilding it 3 more times with the same results. so I went back to the salvage yard and got another quadrajet carb just like the one I have. put it on just like it was and started it up. no more cutting out. took it for a test ride and it run great. that was yesterday. today I added powersteering to the truck. started it up and took off for a test ride. started cutting out as I drove. What do I do now? take the carb off and rebuild it? replace the fuel pump? any help would be great. thanks.