i have a 1998 gmc sierra slt with a 5.7 and a gear reduction starter. my problem: the starter kicks out at times, just whines without engaging at times, works fine at other times. i have removed the starter, had it checked on machine at parts store and it says it is all good. i also took it apart, checked the brushes, gears, drive, etc, all seems to be good. flywheel teeth are all near perfect. could it be just a weak solenoid or is this a characteristic of this starter?