This is on my new 06 GT with 60k miles... Seems like at around 3500rpms the battery gauge spikes and all accessories will cut off until the rpms drop then everything comes back on. By accessories I mean: Radio, interior lighting, and fog lights. Seems to have a new-ish alternator. Current mods are: Ford Racing CAI BBK 62mm throttle body SLP exhaust Sequential turn signals Push button start. Could it be a defective voltage regulator in the alternator?