Check out some of the figures/ciphering that I posted in this thread:
http://www.elcovaforums.com/forums/s...ad.php?t=43055
Most can get 37x12.5 under their truck with no rub by just cranking the torsion bars...that's going to make your ride harsh over bumps though. You'll prolly end up looking at leveling kits like Cognitos UCA kit...couple the UCA kit with some GM Green keys or the Truxxx keys and you'll have a leveled ride with a smooth factory ride.
As for shocks, the Cognito kit I got came with Bilstein front shocks. I had the rear shocks replaced with Bilstein as well...the ride is as good as, or better then, the stock ride. I feel like I have less body roll when cornering at speed then with the stock shocks.