Tinkering:
its a 12vdc 7W GPS device that Im controlling power to.
This should have been mentioned in post#0.
If the data pins of this device are also connected to the Arduino, then you can't just switch off power to the device.
The device could be phantom-powered through the data pins, and that could be a danger to the GPS and/or the Arduino.
Post a link to the GPS, and a full diagram showing all connections.
Leo..