05 psd clutch peddle

My 05 superduty's clutch peddle pushes hard when I'm turning the engine hard and when I do shift the clutch peddle stays down , sometimes it comes up on it's own and other times I have to help it , even though it's down the truck still pulls . I only move the clutch about 2 to 3 inches. I have replaced the master cylinder and it still does it . Should I replace the slave or is it internal ?