You can see the Arduberry schematic here, you might want to double check that nothing is interfering with pins you plan on using. Part of your question depends on which GPRS module you’re using, and what pins those are using.
Are you using the Raspbian for Robots image on Pi? If you are using this image then you can use the serial pins for GPS, if you are using your own version of Jessie, you should be careful because the serial pins are tied up for the onboard bluetooth. They have to be disabled to access them.
You can also try out our GPS shield and its tutorials here.
Thanks for posting, Do let us know if it helps.