1995 Oldsmobile Cutlass • 6 cylinder FWD Automatic • 173,000 miles

I have a 1995 Olds Cutlass recently purchased, I have replaced plugs, wires, air filter, fuel filter and now fuel pump after having it diagnosed. It is still losing power when passing or going up a hill, no check engine codes, gas mileage is reduced, does not stall out. Mechanic says there is still little to no fuel pressure after putting in the new fuel pump. Could this be a the regulator, fuse or relay? I don't know much about cars but want to make sure it is fully checked out today and not sure what else to do. I have also done gas treatments. There is appx 173000 miles on the car.
January 25, 2011.

Use a gage and check fuel pressure. If you test drive in drive instead of overdrive, does that help performance?

Mar 12, 2011.