Pulled the plugs, and they all look fine. I did a compession test while i pulled the plugs, and most Cylinders are around 80 to 90. Number 4 was only 65, and 6 was at 120. All plugs were a tan color with no evidence of being fowled. At the moment I have no codes, but the engine still runs poorly. In park, if i mash the accelerator it falls on its face, then starts to wind. Most of the time it only winds to about 4000. If i ease into the accelerator it will wind up to 5500 or so. What is the best way to check if one of the cats is plugged?

 

that compression is a bit low (and that big between 2 cylinders is a big red flag) anything under 100psi is bad. Put a little oil in each cylinder and see if it goes up (indicating bad rings)