Volvo R1700/R1900 Clutch pedal issue (92 WhiteGMC WIA TD123 9spd)

The other day, a strange issue started with my clutch pedal. The pedal is no longer smooth when I push or release it and the air assist causes the pedal to "kick", as in if I hold the pedal down a bit the pedal will vibrate as the air assist pulses. When I operate the clutch with the truck off and no air in the tanks the clutch petal is very notchy as it goes in and out; catching and releasing as it goes through the travel. The clutch still seems to operate just fine and I can drive and shift, but I've never seen such an issue and I'm afraid if it gets worse I might not be able to operate the clutch. My guess is a master cylinder issue, but I don't want to just throw parts at it guessing. Has anyone seen an issue like this or have any insight?

 

Yeah. The truck is new to me, but it seems to be a rare configuration here in the states. Volvo TD123EA in front of a Volvo R1700 9 speed. It's synchronized and split with an air activated solenoid. The clutch is definitely air assisted and there is a hydraulic master cylinder. on the firewall.