Sudden hesitation and rough idle?

[matts86chev]

I have an 86 chevy c10 with a new drivetrain, well it was new last spring so it has about 20k on it now but all the sudden lately it has started idling really rough when I start it cold and takes a few minutes to sound normal. If I don't wait long enough sometimes it stalls as soon as I shift into gear. It also has been hesitating for the first few miles when I accelerate. I'm not sure if I just need to run Seafoam through it or what! Any suggestions?