I actually had the opposite problem when I was running l28 and 5-speed. When I changed my slave I bought aftermarket the slave rod that pushes the fork was actually too long. The rod, however, had threads on it so it was adustable, so a shortened and adjusted it and it was fine.
In you case, If you remove the boot on the slave are there threads on the rod? was the clutch master, clutch line, and slave properly bled?
also check the pedal adjustment inside.