loss in power

i put a new carb on, it doesnt backfire anyma
ore etc, found out the one i got from big amigo had a sensors wires cut.. but now it runs great, unless i try to go over 50mph it just wont go.. maybe a clogged cat?? anyone else have any ideas? it also sounds like its running on 3 cylinders but im getting spark on all 4..

sounds like vaccum advance to me

two things I would check. . .

make sure the base of the carb isn't warped. . . spray solvent around the base while the truck is idling and see if idle quality changes. . .

Maybe the secondary isn't opening. . .they are vacuum operated, and sometimes they get stuck closed, or the linkage on the back gets disconnected somehow. . .pops loose. . .

thanks guys, ima check into today