I think you have the external slave, arm/fork, pivot ball mechanical mechanism.
Did the clutch fork or arm get replaced with new clutch and pressure plate?
Also did the pivot ball in the bell housing get replaced?
Clutch disengaging force comes from strength of pressure plate + frictional losses to articulate the mechanisms (clutch arm pivot).
I don't think there are many options for heavy duty pressure plates?? Some people make different discs but p/p is limited by weak master/slave and space limitations. What did you replace it with? If GM part or similar its a Luk and they are not real heavy or hard to disengage.
From reading some other posts its probably the clutch arm/fork and pivot ball is worn and adding significant resistance to the mechanism. My 97 master cylinder is a plastic little dingy thing. You can see it flex when you have some one push in the clutch. I don't think they stand up to much heavier actuation forces.
I had a 78 manual transmission/ clutch that kept breaking the all mechanical push rod mechanism even with new clutch/pp/throwout brg. Looking back now it was probably the pivot ball/arm was also worn out.
97 5spd K2500 Ext Cab short Bed ~160K miles.
TM, 3" downpipe & 4" exhaust, remote FSD, remote oilfilter, Gauges: EGT, Boost, Fuel Pressure, B&W Gooseneck Turnover ball, Prodigy Brake Controller. Hi-Temp Hydraulic Oil Cooler Lines.