So have you checked the plenum and cat ?

 

How would I go about checking the plenum and cat?

Also, after another 100 miles on the new plug, the cel came back on again.

 

This is one way to check the plenum http://dodgeram.info/tsb/2000/09-05-00.htm

As far as the cat goes, you need a infrared temp gun, or take it to a muffler shop and have them do a back pressure test, which is the best way to test it.

 

I'm about to do the vacuum test on the engine. I also cleared the code by disconnecting the battery and laying down on the horn. It usually takes 100 miles for it to come back on again. I didn't mention on the exhaust, I took off the stock muffler and I have a cherrybomb exiting in front of the passenger side tire. How much would this alter the backpressure in the cat?

 

I've now driven the truck over 200 miles since disconnecting the battery and holding down on the horn button to clear the computer memory of the p302 code. The cel hasn't come back on, but the truck is beginning to miss again and run kind of rough. It keeps fouling plugs in the #2 cylinder and every time i put in a new champion platinum plug, the motor runs smooth again for 100 miles or so. The truck isn't burning any oil and i'm thinking of trying another plug in that cylinder. Any opinions?

 

Hate to be Captain Obvious here, but you keep on dealing with the symptoms, and not the problem.

Could be worn valve guides, the seals for said guides, or worn rings.

 

Or the plenum gasket that doesn't seem to have been checked yet.