I have a 2004 Nissan Frontier. Last February I had to change the starter out. Last Wednesday I noticed that it was slow to start. Thursday morning it was even slower. I took it by O'rielly's auto parts and had them check the battery and the alternator. Both checked out but when I tried to start the truck at the store it barely crunk and I heard it grind just a little. The person at the store said it might be a bad starter but it would be under warranty. So I got it home and pulled the starter off. Took it to the store and they tested it and said the starter was perfect. I took it back home and reinstalled it and now it cranks fine. I tried shutting it down and restarting it several times with no problems. When I took it off all of the connections were tight. Any idea what could cause the problem or should I just drive it until it breaks and then try to diagnose? Thanks for any help.