Could be the fuel pump relay, which can be replaced for about $10 plus shipping. Could be sediment (rust) in the gas tank clogging the lines and filters. It can happen. Seems to me, considering it cost you nothing, it would be well worth the money to get thee to a qualified Volvo mechanic. Ask aroun...

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 filt...