1988 f150 clutch issue
 

hey guys, 1988 f150 4.9 4x4 5 speed . the clutch has recently been replaced for the most part works good, when I first get in it to drive I have about 60% pedal but it shifts fine , then after a while it goes to about 40% its mostly noticeable when im pulling out the clutch releases real close to the floor and stead of the top of the pedal motion. ive replaced the slave cylinder and what knot ... any suggestions comments or ideas? thanks folks