I have a 97 chev s10 pickup. It is a 4 cylinder. I have a problem. Most of the?

time when I first start it up it runs extremely rough; the whole truck shakes and engine misses and backfires if I gas it. Eventually it is ok, but recently it has even gotten worse and doesn't straighten out. It's like a plug wire is off the way it acts. It has new plugs and wires. Would you have any idea what it might be? Maybe some things I could explore? Thanks a bunch.