how to data log

I assume you want to do some standalone logging on one of your Duramaxes?

Make sure your V8 software and firmware are up to date (july 19 software is the most recent).

Open V8.
Select F5: BBX
Under F2: Scan, add desired controllers, then select desired PID's.

NOTE: If your BBL controllers is blank, you can either click the + button or right click to add a new controller, and in the blank controller box (ECM or TCM) right click again to choose the correct controller from the drop down lost. Once you've selected the controller, the available PID's is on the right hand side. Highlight the PIDs and use the arrow in the Selected PID's window to move them across.

From the buttons at the bottom of the screen, with your FlashScan connected to your PC, select PROGRAM to program BBL into your device....

To physically log in your vehicle, after programming the above....
Connect FlashScan to your vehicle
F1 Scan Tool
F1 Select PID's (if you programmed your device for multiple BBL controllers) and chose the right controller.
F2 Data Logging
F1 Record Data

Cheers
Cindy