rough idle ,vibration

I have a 1991 s10 Blazer 4x4 with a 4.3 v6. My problem is that it has a very rough idle and the whole engine shakes. Also when I am driving it ,it has a vibration that I feel mainly at my feet. The vibration gets worse as it changes gears and is at it's worse in overdrive. It has a 700r4 automatic. Does anybody have any ideas.

Thanks, Ddum8
P.S. Go Jr.

I have a 94 s10 blazer 4wd and mine was running rough and I had to have a CMFI unit put on it, with labor and the part, it ran 688.00. It made a world of difference in the way it runs.

I found the problem ,it was the fan clutch. I could not believe it was as simple as that.