So my check engine light came on after the problems i had with the cat... here is the run down.

Had lack of power to the point 40MPH was all shifting hard and higher RPS to shift well it came down to being a bad car so i hollowed it out cause i cant afford one right now well today i get a check engine light and i get it scanned and its telling me that 1, 3, 5 is miss firing... i pulled the plugs all look good what else could it be? is the O2 sensor throwing it off? i have a 1998 Dodge 1500 3.9 V6 2WD 144k miles

 

Blown plenum?

 

+1... Check your plug wires as well. Try routing them so they don't touch each other or any thing else as best you can.

 

+1 also when rerouting the wires, if they have to cross each other try to do it so they cross at a 90 degree angle. Especially the coil wire. Minimizes the crossfire issue.

 

6 cyl has a plenum also? Didn't know that.

 

yep 6 has plenum. Same engine design and family with 2 cyl chopped off.