This link takes you to an outfit that has an adapter which plugs into your OBD port on your truck and adapt the port to a USB plug. This means if you have a laptop all you have to do is get the software and you laptop becomes a scanner. The board is available in kit form if you want to save money and assemble it yourself, The kit $45 dollars plus $6 bucks shipping and handling
This link is to a device which mounts on your dash board and plugs into your OBD port, with it you have real time gas mileage, average gas mileage, tach, speedometer, gauges, etc, it reads diagnostic codes and you can clear them.
The top photo is the USB adapter, and the bottom is the Scanqauge II
My Carbon foot print is 57 tons per year, and that doesn't count my fart gas.
I spend my carbon offset money on my 1995 F150 Flareside with a carbon spewing 5.0L V8.