Yeah GPS does work in Pakistan. There are free open source maps available for Garmin brand GPS devices. I am using it since 2009 and fairly detailed maps are available. I also used it Lahore and it helped find out my uncle's house in Garden Town after I missed a right turn on canal while coming via motorway.
This thread might be helpful:
https://www.pakwheels.com/forums/car-entertainment-electronics/111704-my-first-gps
If you Google, you will find a couple of companies dealing with the equipment for cars, in-dash stuff as well, but they are too expensive, just for the map they charge about 130 dollars.
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