Hy IDidIt, I have been meaning to get back to this for days, but life kept getting in my way. After checking a loose booster of the same type as your truck has, I find that the atmosphere air enters the booster through the back of the booster where the pedal shaft goes in. My conclusion is that the vacuum two speed control is somehow allowing the vacuum to escape. Possibly the vacuum shift diaphragm has a hole in it, hope that helps.
