Use a control arm kit for the front. It is CRITICAL to narrow the front track width on these trucks if you are going lower. Stock width control arms will put the front tires in contact with the inner fender lips and ruin a nice set of tires.
Front co tool arm kits that narrow the track width are Stone fab, IHC, and CPP.
I used IHC and am happy with the result, but only got 3 inches of drop by design. You're looking for 4 so you might combine IHC with a 1" drop spring or coilovers to get an extra 1 inch of drop.
For the rear, the 2 door and 4 door tahoes are different from the trucks and burbans due to leaf spring measurements and front hanger design. You have spec'd a 6 inch drop so hangers are not the best option. The fastest way to 6 inches of drop is a flip kit with c-notch. I think the flip kits ARE the same across all gmt400 offerings but you should confirm before buying a kit, because there may be a difference in the c-notch given the 2 door tahoe frame is different.
Here's my 4 door with 3 and 4 inch drop. IHC control arms up front and bell tech 4 door tahoe specific hangers and drop shackles. My tires are quite a bit larger at 31 inches tall vs yours. At the end of the day I've eliminated fender gap, which was the plan all along. As a side note it sits much higher now than it did with 2 inch drop all around and stock wheels and tires.
