I've had similar problems... one time it died on the highway for no apparent reason, then restarted fine an hour later and ran flawlessly. Mechanic at the dealership put it down to a blocked carb breather pipe. A few months later it began dieing intermittantly but would restart immediatley - this time it turned out to be a bad coil, but you've already replaced yours. Try checking all the breather pipes below he engine for accumulated road grime etc.
