Nope, no interrupts, the sketch is pretty straightforward and simple. And I've verified it's not being reset through use of an uptime counter. I still have to test the other machines though, but the weird thing is, it's very much power supply related, since I've ran it for over 12 hours without it crashing the serial port when there's no external power supply being used. Also verified on a separate mega r3 that the problem doesn't happen. Makes me want to try the older arduinos with FTDI based serial chips, but I don't have any of those unfortunately. When I'm able to test the other machines that should be insightful.