I have Lexus 2001 IS300. Just had fuel pump replaced, felt really good driving , even the motor was working smoother, nice and quiet. Drove for a week and suddenly lost power again, it felt the same as before when fuel pump died. What could it be? Could that be a defective pump or is it something else?

if not a factory oem pump, they often stink. if factory, check the wiring for shorts and also replace the fuel pump relay if that wasn't done