I hear ya. I've got the same situation (3" rear blocks, 2.5" level kit in front). I originally had stock 17s w/the smallest tire GM could find, so going to the 20s helped fill up the gap some. It is still begging for a taller tire. I'm going to wait until these wear out a little, which may take longer than I thought.
Yeah the bridgestones seem to be pretty good, they are quiet, and they do pretty well in the snow up here. I'm looking at getting some duratracs, only because I want bigger tires to fill in the gap after I installed the leveling kit with the rear blocks. Only have 20,000 miles on the Duellers though so not a huge rush. May try to sell them though.
Saw your truck in Ajarman's thread. Looking good! Post up some more in an album, if you can. How do you like the Bridgestone Dueler A/Ts? How's the ride and noise level? I've got the stock duelers (H/L) and they have been great and wearing evenly. I've been looking at the A/Ts for my next tire, maybe in a slightly bigger size (275/60R20). They look good, and I only go off-road every now & then. Let me know what you think of them, and the mirrors as well. Get some pics up, we'd like to see more of that truck!