If you buy a V2, you can use it to diagnose most GM vehicles. You can also tune 2 vehicles before you have to purchase another license ($125 each for additional licenses). The V2 uses one license per vehicle and comes with 2.
I would recommend purchasing from the vendors here. Most will give you a tune if you purchase a V2 from them.
The tunes for the LBZ and the LB7 are different, don't mix and match. The tune should be written for the specific vehicle, based on factory options, fuel tank size, power adders, etc.
One thing you may find is that the tunes in both your trucks are locked. Some tuners will not allow folks to see what is in their tunes, and lock them down so they can't be pirated. These tunes are like software, and should not be stolen....it's bad form to say the least.
Good Luck, have fun. :thumb:
Edit: You can diagnose engine issues, transmission issues, and clear all codes, but it will only talk to the ECU and TCM. It does not communicate with any of the other computers in the vehicle. It is not a Tech II.