Infamous Hesitation

so i have the hesitation in my 89 420sel that so many people have. so far i have checked;

plugs
vacuum leaks
new o2 sensor
new spark plug wires
newish EHA
checked the fuel distribution fuel lines for leaks

and so far i still cannot figure out the problem. i was running pretty heavy on gas consumption about a month ago so i replaced my o2 sensor, and the problem still persists. THis leads me to believe somewhat that it it a clogged catalytic convert. I am not sure what the car is supposed to sounds like if the cat it plugged, broken, etc but from listening to it underneath the car it sounds like there is a weird burble/rumble coming from the cat. The sound is not coming out of the tail pipe, and it is not consistant with normal firing. almost like a piece os moving around and burbling inside.

is this a common sympton of a bad cat?

also, i'm not sur eif this is a seperate issue or related but i was driving for about 45 min and all of the sudden my car jumped out of 4th (at about 65mph) and dropped down into 3rd. This continued to happen at an accelerating rate the more i drove. anyone have this issue?

fluids are good, new trans filter and new fluid.