it is most likely the clutch booster itself. I just recently replaced my clutch booster for the same reason. I had to remove the dash to do it. Some have been able to do it with the dash in but I believe the support bar behind the dash might have had slight changes from year to year that allows clearance for removing the booster.
Follow the vacuum line near the clutch master to where it connects to the intake manifold. You can eliminate the clutch booster by capping this nipple on the manifold.
Formerly: ZEVAN (Ca), Evan3zx(ca) Xbox live GT: kidding Me