To locate it, you'll have the best luck by:
1. Consulting your owner's manual: This is the most reliable source. It will have diagrams showing the location of all major components, including the fuel filter.
2. Using a repair manual: A Haynes or Chilton repair manual for your specific year and engine will have detailed diagrams and instructions.
3. Online searches: Search for "[Your Engine] fuel filter location 1994 GMC Vandura 2500" on sites like YouTube (lots of videos showing filter changes), or automotive forums. Be cautious and verify information from multiple sources.
Generally, fuel filters on vehicles of this era are often found along the frame rail near the fuel tank, but sometimes under the vehicle. Always be cautious when working near fuel lines and take appropriate safety precautions.