We just replaced the elctronic fuel pump in a 94 Gmc Vantura 2500 350 engine. It will run sometimes a few miles and then quit. After a few minutes it wll start. Now it wll not start at all. We have also replaced the fuel filter.
Can anyone help us identify the problem we are having with the fuel? Thanks.

Performing the tests, in the link below, should help:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-11.html#post2123675

Be sure to test all under hood and under dash fuses with a test light or multimeter. Likewise, test the fuel pump relay. Find out the procedure to check for codes.

Even though the link below is specific to Hondas, try developing a similar understanding and procedure for your GMC:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-selected-other-vehicles-46563-7.html#post1245523

If the problem persists, check the ignition switch for wear, pitting, or melting--replace, if necessary.

If your 350 has a carb there may be a second fuel filter inside the carb body where the fuel line enters. The fuel line needs to be removed to access the filter.