00 v6 3.9 will not start

I have tested battery its good, alternator charges it and runs. If i remove the battery leads and then reconnect truck starts. Once started though the battery amp meter pegs to max (all the way to the right at 18) and stays till i shut the truck off. After 24 hours after the reconnecting of the battery and starting it will not start again until i remove leads and reconnect. I was thinking the alternators regulator, cat or computer, the last being the last thing i really want to have to replace.