Sled serial is DCE, but also has 12V (Remote Amp) on pin4, and a couple of the handshake lines are actually Dimmer and Mute, but I forget which.

I would bet that most GPS receivers are also DCE, so you would need to cross TxD and RxD in the cable.

Basically, you need (assuming GPS is standard DCE)

Sled<->GPS
2 <--> 3
3 <--> 2
5 <--> 5 (Ground)
4 <--> GPS 12V in. (Assuming your GPS accepts 12V in - otherwise a power regulator will be req'd)