Below-spec acceleration - Why?

My car seems to have a slight performance issue. Everything functions and runs normally, no stalling, rough idle, or failure to start. However, the car accelerates slightly slower than it should. 0-60 takes 10+ seconds (even with brake launching) when it should be 8 seconds or less. There's plenty of tread on my tires and the transmission seems to shift fine. It has a new fuel filter, air filter is clean, catalytic converter is not clogged and the spark plugs are brand new. I know it's not a major issue, but if I'm getting V6 fuel economy, I'd like to have V6 power available too.

The only thing I can think of is a fuel pressure problem. I had the fuel pressure tested for a different problem earlier and they said it was about 4 psi below spec, but my car isn't giving me any of the classic fuel pump failure signs (difficulty starting, losing power while driving, lurching, etc.). Would fuel pressure 4 psi low give me my performance issue? Could it be something else? How do I diagnose this?