Jeep Running Rich

I am in need of help with my Jeep. Ok, so I have a 1987 Jeep Wagoneer Limited. This isn't the large Wagoneers that some of you may be thinking of. This is the Wagoneer that looks like an XJ. Anyways... The Jeep is an offroad beater, and it has been put through a lot of abuse. Believe me it has. So my problem is that the Jeep is running very very rich. It seems to be at a full rich because its only getting around 3 miles to the gallon. Yeah, pretty bad. Another thing the Jeep is doing, which I am not sure if this is because of the full rich or not... The Jeep is missing and sputtering when it's below 2,500 RPM. When I am accelerating, as soon as the Jeep goes past 2,500 RPM, it has all its power, runs great, and seems normal. As soon as soon as the Jeep dips below 2,500 RPM, it runs badly again. Does anyone have any ideas? I am so stumped! Please help!
Thanks!

There is a good chance that your cat is plugged. It happens quie often to the older vehicles.

with it running that rich it should be billowing black smoke. Check your vacuum line to the map sensor. If you've been running rich for long you're also going to need an O2 sensor.