depending on what your truck has set up but my mud truck with no emissions i have brake booster which should be manifold vacuum, pvc which should be manifold vacuum and distributor which again should the one marked "cap" manifold vacuum (for best performance, if you want better emissions you have it to ported)
but your trans should be hooked up to manifold vacuum also. im not sure about your carb but if you have the engine running put your finger over the port and see if theres vacuum