High pitch squeal

I just replaced the spark plugs on a 2003 ford escape 4x4 3.0 v6. I replaced all the gaskets that came in the intake gaskets kit. i was getting a code saying there was i miss at number 1 and number 6 cylinder. I was also getting a PO420 code saying something about an o2 sensor. I cleaned the o2 sensors and now there are no codes. the problem is the motor runs fine. but i cant drive the car. i can only get it up to about 30mph. when i step down on the gas the motor revs up then there is a loud squeal. i have checked everything. I cant fine a vacuum leak or anything. i checked the trans fluid its a little brown but its not low. im going to change that this coming weekend along with a fuel filter. Could the cat be clogged? if so witch one. i don't have a lot of money so i cant put it in the shop. if someone could give me an idea of what could be be going on or how to check the cats while they are on the car that would be great. and if it is a cat whats the best way to replace them. i know the front bank is $588.00. please help me.

i had to replace my back cat. it cost me 350.00.

that does not sound like a cat. It would smell like burning sulfer or eggs. find what that squeal is. Get a compression tester and test the compression on the cylinders. Could be many things as of now. vac leak fuel problem many things. Even a stuck brake caliper.

There's a post in Escapes title "EGR valve". The V6's have 3 cats. One on each manifold and the main rear. The two uppers are junk and send their guts to the rear clogging it. When it gets clogged, back pressure comes back up to the EGR valve and sometimes makes squealing noises, and sometimes actually caused the valve to explode! The exploding valve actually happened to mine. Replaced the EGR valve and back cat. Did nothing with the front ones that are now empty and don't cause me any codes for emission testing required for our area.