[jermasaurus]

Why do you have these problems with a sweet lookin truck like that? (Assuming the one in your avatar is yours)

What F.Monroe said is right. Also a vacum leak can cause that issue. Carb to intake gasket perhaps?
I bought a cheap gasket at autozone and it just didn't seal.

Spray that intake down. If you dont find any leaks, then I would look into adjustments or a rebuild of the carb depending on it's age,