2000 Other Isuzu Models

Im having trouble starting my 2000 Isuzu Hombre. With 140,000 miles on it I replaced the starter 2 years ago with a brand new (not remanufactured) autolite starter from checker auto parts (CSK). I also replaced the alternator about the same time. My starter started having problems first, then about 2 weeks later my alternator stop charging the battery. With a fully charged battery, when I turn the key, the starter tries to crank the engine over but stops. It cranks for about 1 sec. Then goes silent for a sec or two the either cranks for 1 sec or grinds the teeth on the flywheel. You know the sound a starter makes if you try to start a vehicle that is already running? If I rapidly and time it right, by turning the key very quickly, I can get it started. Ive changed the oil, checked the negative battery cable, checked all of the connections to the starter to make sure they are tight, and I even hooked up a remote starter switch to the solenoid and it does the same thing. Which leads me to believe it is not my ignition switch. Have any ideas? I'm lost and the auto part store lost my warranty information on this $200 starter that doesn't work now.