Suggestion:
If you have any mods that have electrical wiring passing through the firewall I would check for chaffing. Also look at your fuse box and make sure you do not have any loose fuse taps, wires, or fuses for that matter out of place. Definitely sounds as if you may have an electrical problem. You may even want to disconnect your tuner and give it a try just to make sure its not the problem. Do a complete visual of your engine bay and check all electrical connections before your start replacing parts.