92 B250 Ram Van running rich/black smoke/hard start

I bought this van about a month ago. ran great, ran rich. I've been busy and lazy, and have put off attending to the "running rich" problem, and it has gotten progressively worse. A few days ago I took it out on the freeway and had a really hard time getting it to accelerate to highway speed. I kept on the gas, and black smoke was spewing. Then it suddenly coughed up a bunch of smoke and found some power, like it was blowing it's nose. Then it ran fine for a few days, and now the problem is back, and I've really got to do something about it. Any ideas? or a check list? thanks scott

Plugged cat/exhaust?

-upstream o2 sensor
-map sensor
-fuel pressure regulator
-ignition secondary wires

just a few possible causes.

Is engine light on if so any codes?

You will ruin your cat and possibly your o2 if you keep driving like this.