StreetDeck allows you to use a NEMA dump from a GPS for testing navigation.
To use a simulation file, you must place an appropriate file in the Program Files\StreetDeck directory call GPSSim.txt and set your GPS to "Use GPSSim.txt" in navigation settings in StreetDeck.
To create a simulation file, on a GPS enabled version of StreetDeck, add the command line parameter -recordGPS, then drive around to capture some data. A new file will be created under My Documents\StreetDeck\Logs\GPS each time StreetDeck is run. You can simply move and rename one of these files to GPSSim.txt as indicated above to review the simulation. Simulations run slightly faster then the speed at which they were recorded.
To prevent you from being locked out of certain modules while testing, you should also add the -testmode command line parameter to disable the safety features of StreetDeck that are based on the GPS speed read from the simulation file.
RedGTiVR6 - I have uploaded a very short video showing how to change your navigation settings from within StreetDeck to point to this new GPSSim.txt file. I needed to make this for someone else and figured it might be useful for some here as well.