The mechanical LRD in the Tahoe's is a tried and true bulletproof one. I've had 3 with extensive offroad use in two tahoes and a silverado. The 21's is strong. But as mentioned, if you're looking for ground clearance, Z71 or not, the Tahoe is not your vehicle. While the air suspension can give you 2 inches in approach, it won't do anything with clearance of the suspension parts.