Where does the vacuum line from modulator valve go to on a 1994 1500 Chevy pickup?

The vacuum line from the modulator valve on a 1994 Chevy 1500's automatic transmission goes to the intake manifold. Specifically, it connects to a vacuum port on the manifold. The exact location of that port varies slightly depending on the engine, but it's typically near the throttle body or other vacuum sources. You'll need to consult a shop manual or a diagram specific to your truck's engine (e.g., a 5.0L, 5.7L, etc.) to pinpoint the precise location.