Various Problems/Possible Catalytic Converter

I am experiencing various new problems with my 86 GMC Safari. It started using way more gas, losing power, using more oil, and seems to be spitting black soot out the tailpipe. I just had the spark plugs and wires changed, then it started doing this. Someone told me it was possibly a catalytic converter issue, I was just wondering if anyone had any suggestions or previous experience with something like this.

I don't know what the problem might be but your astro van is 20 years old, you should just be glad you got that many years out of it.

Phtt! That's nothing out of an Astro.

Are you getting a CES or SES light? If so what codes are set in the computer?

my 86 Safari had over 250k miles when i sold it two years ago and last month it passed me on the freeway. i'd know it anywhere as it was a customized van and still had the mudflaps and crack in the real taillight it put on it.

how long since a full tuneup, including those pain in the butt to change sparkplug wires?