HU isn't going to have that much effect here. What are you running the SA's at resistance wise? 1, 2 or 4 ohm?
If running @ 1 Ohm the Williston Dyno shows that amp pulling 338 Amps to make 2920 watts which is 61% efficiency, later he provides an efficiency rating @ 1 ohm of 72%. (Maybe after the amp had warmed up) (14.05v x 285.6A) / 2916. Either way you look at it even at half gain, unless you're measuring with a multimeter and have a general idea of what the amp is outputting that amp at half gain, it is still drawing enough power to shutoff your Tacoma. If you went into protect at 9 Volts you basically ****** your car's battery dry before the amp went into protect mode. I'd put a multimeter on the speaker output and try to get down to 1000W output until you get some electrical upgrades, otherwise you'll be forced into replacing the alternator soon anyways once the internal rectifier fails on it.