When you say "stiff as hell" I can guess you mean the pedal. The pedal is not the clutch.
Right string wrong yoyo.
Is it hydraulic? By that I mean does the pedal operate a little master cylinder which operates a slave cylinder at the clutch?
I know of a few occasions where the clutch disc has stuck to the fly wheel but that will not make the release mechanism any stiffer than normal.
When they replaced the clutch just what did they replace? The clutch disc for sure but did they check or replace the pressure plate? That's what actually releases the clutch.