I rebuilt a Montreal clutch master cylinder sleeved in SS by Karp's earlier this year for a friend. The work quality was top notch. The clutch hydraulics have so far functioned as intended. It's my understanding though that Karp's does not rebuild cylinders, only sleeves them.
Sounds like this could be a booster issue or the M/C pushrod is adjusted a bit on the long side....but sometimes the pedal goes hard and you don't have much stopping power.