The Lat G channel is data from the G2X internal G meter. The GPS Lat G is calculate G data based on GPS information. GPS G data is not affected by the pitch and roll of the vehicle.
The G2X Pro manual contains a Terminology section (around page 13). This typically covers both the G2X and G2X Pro. www.g2xpro.com
There is an existing forum on the g2x website, which can be found at www.g2extreme.com
which contains a variety of questions and answers.
If you have any additional questions, please let us know.