Do you still have your old filter?
If you do cut the can open and have a look at the media inside.
If not it may be worth the cost of a filter to cut the one you have on the engine now.
It inside may show signs of the reason for low pressure,ie metal in the filter.
90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews