1995 Chevy Truck clutch will not disengage

Installed 2 new clutch kits, new slave, new master cylinder, new clutch fork and clutch will not disengage.
when mechanic removed old clutch found a welded extension on slave and the forks looked to be modified. The local parts store was not able to offer any advise. I purchased the truck this way and have had it for over 4 years. It was working fine till about 3 weeks ago when we started to notice it slip and had have a hard time getting it into reverse.
any advise.