Engine loses all power - rpm related

[87 hardbody 4x4]

After fighting this problem for a long time, I discovered that if I would push clutch peddle in 1/8" my truck ran fine. So I looked at the switch on the top stroke of the clutch peddle and adjusted it so it never touches. Runs fine now, no more short shifting,doesn't lose all power at certain rpm in every gear. Not sure what the purpose of the little switch is for. Hopes this helps others.