Any engine misfire might activate the "knock sensor" which automatically retards the engine ignition timing and you lose power. But you don't mention having a yellow check engine light on or noticing any engine misfire. It would be nice to drive it down the highway with a fuel pressure gauge attached to the fuel injection rail so that a friend could monitor the fuel pressure as you drive. Maybe the fuel pump is giving out?
However, even if the pressure reads right, the pump may not be able to supply the full fuel volume necessary which is substantial if you'll read the tech article below.
http://www.aa1car.com/library/fuel_pump_diagnose.htm
