Another thing to check: When installing a new fuel filter, it's very easy to kink the short fuel line between the tank and the filter. That leads to weird and unpredictable fluctuations in fuel delivery, and mimics a fuel pump or fuel pump regulator going bad. Maybe that happened when your fuel fil...

I've got a 1996 Volvo 960 w/2.9L engine 182K Miles. This car has one fuel pump(In-tank). About a month ago it started occasionally having "spells" where it would sputter and/or stall when I hit the throttle but only occasionally. Between "spells" it ran PERFECTLY at any throttle ...