To be absolutely certain, you should:
* Consult your owner's manual: This is the best resource for precise location information specific to your truck's engine.
* Look at a repair manual: A Chilton's or Haynes repair manual for your year and model will have diagrams showing the starter's location.
* Search online: Use a search engine with keywords like "1994 GMC Sierra 1500 starter location [engine size]" to find images or videos showing its position.
Visually inspecting the engine bay after removing some plastic covers (if necessary) is the most definitive way to locate it once you have a general idea of where it should be.