Purolator fuel filter would be fine. I would stay away from delco anything lately due to parts out sourcing. I run WIX filters for everything on my vehicles with no issues.

The shrader valve for fuel pressure release on the 3100 is near the power steering pump, look inwards towards the intake plenum. It is sticking out the side of the fuel rail, sort of a pain in the butt to get to because there is an engine lift bracket and a power steering hose sort of in front of it.

I finally have the opportunity to change the fuel filter on my GP, but I notice you highly recommend to use a AC Delco fuel filter; however, I have a Purotator fuel filter. What should I do? And can you pinpoint the schalve valve for me in a photo for my GP 3.1L V6 128580 km. Please respond promptly. Thanks!