I have a Chevy Suburban C1500 1/2 ton 5.7L SFI V-8.When I take off it sputters and misfires and doesn't run like it's firing on all 8 cylinders.When I floor it,it takes a second but it clears up and throws me back in the seat and runs great so long as the pedal is still to the floor.Once I let off it goes back to sputtering and misfiring and the whole truck shutters.The fuel pump has been whining really loud for some time.What could be the cause of this and if it's the fuel filter,where might this be located?