I have a 1990 chevy 1500 4WD with a 350. The truck has been parked for almost two years, except being started and driven short distances periodically. After sitting for awhile the clutch would always have very little resistance when I first started it, but after I pumped it a few times it would stiffen up. Now it goes to the floor with no pressure and never tightens up. I have changed the clutch and slave cylinder not long before I parked the truck, so I don't think that would be the problem, any ideas?