I'm not the one to discourage troubleshooting, but if your hazards and signals work and the brake lights don't, the #1 suspect is the brake light switch. They are cheaply made (even originals) and don't last forever. They are cheap to replace. Replace it, and on 1988-1993 there is an adjustment procedure before it will work correctly.
Here's a thread about adjusting the 1988-1993 GMT400 brake light switch:
https://www.chevytalk.org/fusionbb/showtopic.php?tid/180723/
Once you've got the new one installed, adjusted, and working - pop your old one open and discover the set of broken leaf switches/contacts in there.
Richard