The vacuum modulator line comes up from the tranny on the driver's side and goes to the intake manifold right next to the oil filter. Theres a u-shaped rubber hose that the plastic line pokes into. Then the u-shape goes on a nipple on the intake. I knocked mine off once doing an oil change. I had a rough idle and the harsh shifts you described.
Experience is something you don't get until just after you need it.