It could be at the vacuum rotory switch, gang plug, vacuum actuator, vacuum hose, vacuum reservoir may have a crack, etc. What I've done in the past is take a propane bottle with a long vacuum hose on it and and just crack open the valve a little running the tip of the hose around the lines until I hear the engine rev up a little. Make sure both doors are open and your outside so you dont build up gas inside the cab or garage and no open flames or cigs. Just move slowly as it will take a few seconds to reach the engine. You can do the same under the hood but might need to give it a little more gas, but dont over do it.
2001 Ranger Edge 3.0 V6, 5 speed M/T
Limited Slip Differential, James Duff Traction Bars
Kumho 30x9.50 15 MT / Black 297 Series 15x7 Rims