OK here is the current situation, and im going crazy. I have a 1998 Ram 3.8 6 cyl. the check engine light was on and pulled a bad O2 code, the truck has 120,000. I ignored it for a bit however ONLY WHEN WARM the truck is starting to loose power mostky up hills and at stops, and will sometimes backfire when I loose power. I put it in Neutral and rev it up, let the RPM;s come back down then put it in drive it goes back to normal. Truck has always been a dog, so I figured converter was plugged... I took it off and half the guts were missing from the inside of the cat... I just cleaned it out a little and put it back and the truck is still having the same problem... I just figured it was the cat, but obviously not... could this be a plugged muffler, or any other suggestions? Im lost here....

 

I know a guy who has an 01 that had a plugged cat causing the truck to have similar symptoms, he gutted the cat and put it back and the problem was solved. That could be your problem, but I think you'll get more help in the 2nd gen section. Post over there or do a search, I'm sure someone can help you out.