Always someone with the cats clogged issue. That is about the last thing to check for, there are a dozen other things that can cause your problem, all of which if ignored with cause the cats to clog.

Exhaust every other diagnosis first. I would suspect low fuel pressure from a weak pump or plugged fuel filter are your mostly likely culprits. A faulty MAF or plugged air filter would be high on the list too. A misfire can also cause your issue, but would be accompanied by codes and shaking.

 

I know this thread is old. Has anyone found a solution for this. I have. 99 exp 4.6 same issue. New plugs, coil pack, wires, and tps. It has a rhythmic low idle in P low in D. Bogs with gas.

 

On the passenger side valve cover, I removed the PCV valve and found the 3" rubber hose sucked shut where it attaches to the PCV valve. Replaced the PCV valve and rubber hose, runs unbelievably strong. I am happy to now floor it to wide open throttle and it revs all the way out to full power now!

 

PROBLEM SOLVED