S10 clutch help!!!

hey, i need some help with my clutch, when the truck sits overnight or doesnt get drivin for a hour or so the clutch looses all pressure. then i will have to sit and pump it for a few minutes to get enough pressure to get the truck into gear. im going to be bleeding the clutch in a couple hours to see if that works but was just wondering if anyone thinks tere could be somethin else wrong with the clutch.

might be a bad slave cylinder