[abaird]

Is your battery bolted down? Make sure battery cables are clean and tight and are not contacting anyhting when the car moves. Try starting the car let it idle and open the hood. Give it a wiggle test. Grab different wiring harnesses one at a time and give them a good wiggle. Start with the battery cables. See if something makes the car die. I have heard a similar story to yours and it turned out that the battery would actually shift in the tray and contact the body when the car made a right turn.