Basically, is the deficiency correctable in the sled itself,
Yes, but you have to actually look at the sled and see how it's wired, and do some quick tests with a wire continuity tester. Once you look at it with the tester, it should be dead-obvious exactly how the thing is wired up and which pins are doing what.
do I have to get power to my gps some other way?
One of the pins on the connector will be connected to the blue Amp Remote wire. That pin will supply 12 volts positive. If your GPS can take 12 volts positive on that pin, then all is well. To get the ground (which is usually pin 5), either figure out a way to ground the pin (not sure how easy this is on a miswired connector) , or change your grounding to use the serial cable shield instead.
All of the above should be dead-simple once you actually look
at the connector on the sled. If you don't know how to use a continuity tester, or you don't know how to correct pinouts on a miswired connector, locate someone nearby who knows about this stuff and can help you.
Just keep in mind that the only serial communication pins the player uses are 2 and 3, (and 5 for ground if it's wired right), and if you hook up the GPS to the player it needs to only use those pins. Anything else would need to be power. If the GPS is trying to use handshaking pins, those need to be disconnected.