The problem was the check valve in the vac line running between the Intake Manifold and the reserve cannister. It had not been replaced, and apparently not checked.
Does anyone know why there is so much dirt in the vac system? I thought it was a closed system.
1988 F150 Custom 4X4 300 - 6 5 spd trans
1992 F150 XLT 4X4 300 - 6 4 spd trans
1995 F250 XLT 4X4 351 5 spd trans