There are lots of China made Walbro 255 knock offs out there. Be sure you have real USA made pumps....Racetronix has them......wouldn't trust any from Fleabay!
Since your fuel pressure fell make sure your filters are the proper ones and that you don't have a carb style somehow accidentally sent out. Also make sure they aren't knockoffs. Not sure how you tell. Dedicated quality (Bosch) relays or similar only.
Are you on pump gas or e85?
I'm going to run 2 of the Walbro 400/450lph e85 pumps for mine. Should support 1000rwhp+ on e85 with -8AN feed line.