Zeeya2000,
The free Alignment is a Warranty issue and it is only good for a registered vehicle. If the dealer does any work before you sign the papers then that work does not affect your warranty claim. As G Man stated, the vehicles suspension needs at least 500 miles on it to allow the suspension to settle in. If you have never personally brought in the AV for the courtesy wheel alingment then you have up to 7500 miles to get it at NO CHARGE.
Don't tell the dealer that you tweaked the torsion bars yourself. The issue that GM is looking for is the vehicle pulling to one side. Just tell the dealer that the truck has a slight pull to the left or right (pick one) and that you would like them to perform the complimentary 4 wheel alignment.