Love seeing all the 4 door tahoe people showing up here these days.
I'd bet the body is shifted over on the mounts. Basically every body on frame vehicle is off at least a little, and it's usually discussed on forums for cars with tight wheel well clearance like it's an issue unique to their platform. For example, almost every late model B body impala SS/caprice/roadmaster/fleetwood is shifted over close to 3/4" in the same direction. With that drop, you're running a flipped axle. The way most of those kits are set up, you can actually move the axle on the springs a bit to center the axle up to the body. Might try that, as moving the body on the frame is a massive pain and is hard to do with any accuracy.