86 350 ram van rough idle

I have a problem.. it starts fine but it has a rough idle. It feels like one of the spark plug wire is connected wrong but i double checked it. What steps could I take into fixing this problem. And also the timing is not right but when I try to adjust it by the distributer it dies when the timing is set correctly.. but if I adjust it back where it was normally it wrongs fine beside of the rough idleing. Could my problem be the carburetar. Fuel pump dirty?

1. Timing chained jumped a tooth?
2. Vacuum leak?
3. Cracked distributor cap?

How does it run off idle (driving)?
Year, engine?