I just saw that you had to solder all sorts of things

Not all sorts of things, just pins 2, 3, and 5 of a serial cable.

And if it were a regular GPS unit with a regular serial port, I wouldn't even have had to do that. The only reason I had to solder was because my GPS didn't come with a serial port, it came with a Palm3 connector. So I had to solder onto the three pins on its PCB that corresponded with the three pins of the serial data on the Palm3 connector.

It's possible that a straight-through serial cable would just work for you. But if you run into trouble, just open the hood of the serial cable and pull all pins except 2/3/5 and try swaps of 2/3 until it works. (2/3=rx/tx, 5=gnd).