301-304 are misfires, plug 1 and 4, should not be there since you changed everything...
you say it starts easily..but anyway, what voltage do you have when it charges..should be 14.2 14.6 volts with engine running. Low voltage causes misfires and random operation...but of course, after a while, it would not start....
but 604 is rather rare....Internal control module RAM error.....can't say more than what is here:
www.avigex.ca/kia/P0604.pdf
....and at 64,000 miles, I would be very inclined to prepare for a new timing belt, if not already done. It can have slipped a cog or two already...an inspection of the timing marks should make or bust this as a cause of present problems...
