I believe the 436 and GPS is pretty much a plug and play thing. You might check your profile in the Location Settings tab and confirm the Baud Rate is 4800 just to be on the safe side.
The manual is a little ambiguous on the 436/GPS Baud Rate, but I know the 536s are pretty fussy about that.
Also be sure your GPS device has a clear view of the sky so it can receive the satellites. They say you can confirm GPS operation by turn on the full database, disconnecting the GPS and entering a zip code of 90201 which is Los Angeles. Then turn on the scanner and see if the Los Angeles "stuff" loads. After that, re-connect the GPS device and see if the "stuff" more appropriate to your location loads.