There is an inspection cover underneath the bell housing. Remove this the inspection cover. While you are under the truck have someone disengage the clutch (press the pedal to the floor). You should see the slave push the release arm and you should see the clutch plate pull away from the friction disk and if the truck is in neutral, you should be able to rotate the friction disk (be sure the hand brake is on and the wheels are chocked when you are under the truck). If the clutch release arm isn't moved by the slave cylinder then there is something wrong with the push rod adjustment or the master cylinder. If the release arm moves but the cluch plate doesn't move or the friction disc doesn't free up, then there may be something wrong with your clutch, or the release arm is not pivoting properly.
Why did you replace the slave and not the master?