2004 Tahoe Auto with FF V8 4WD and 213000 on the clock.

Problem I'm having is the brake lights aren't working--the center high mount stop light (CHMSL) and the brake lights don't respond when pressing the brake pedal. The tail lights are lit up, but don't brighten up when brake pedal is depressed. 

What I've done so far is...

1. Check under the hood fuse for power. Fuse is good, getting power.

2. Checked CHMSL and vehicle stop fuses inside driver door for power when pressing the pedal and nothing.

3. Check the brake fuse in driver door area and that has constant power whether the pedal is pressed or not. Is that correct. I even replaced all the aforementioned fuses as well...nothing.

4. Replaced stop light switch on brake pedal since I accidentally broke the old one inspecting the internals. Car has a adjustable pedal, so I bought the switch that's for that setup. Brake lights still not working though.

5. I even swapped out the bulbs and the circuit board on the rear passenger fender just to see if anything would change... nothing. I did both of these independently by the way.

6. Cleaned up grounds under the driver door on the frame with some sandpaper since they were rusty anyway, nothing. I did notice one of the grounds had a tiny bit of corrosion. Didn't get around to replacing it because I had to stop work.

7. Don't know if this has anything to do with it, but I do have a C0550 code which leads me to replace ABS control module needs replacing. This related?

I'm thinking of just replacing the harness that plugs into the tail lights and the CHMSL itself. Should I bother doing that or no?

Could the issue be the PCM?

Thanks for the help.