This 70amp relay activates the fuel solenoid on years 94-98.5 12valve. If this relay is bad your engine will crank fine but will not start because the fuel is not getting to the engine. For the minimal cost, you may consider keeping a spare in your truck.
Also- check your blue wire fusible link (available) at the pos battery terminal before replacing this relay, if corroded or burned it will cause the same symptoms.
This relay is physically different than stock, the mounting is slightly different. Electrically it is identical. Some stock relays are a double relay that includes the fuel heater relay. You can unplug the fuel shutoff side only and install this relay to avoid having to buying the double relay.
This relay mounts near the firewall, see the second picture for visual.