I have a '94 GMC gasser with a 5 spd that was making that squeak, after MUCH investigating and spraying this, lubing that, etc. It turned out to be a pivot ball inside the bellhousing that was the source of the noise. I couldnt believe it since it sounded like it was coming from inside the cab, but honestly the noise went away, never to return once that 16 dollar part was changed.