The 6.2 is faster than the 5.3, but not overwhelmingly. The 5.3 doesn't feel underpowered in daily driving at all.
With the exception of the valve deactivation feature, which I think was a retrofit, the entire powertrain on the 5.3 is very established. Old, yes, but not super high tech, doesn't break too much, easy to fix when it does break, lots of parts available and mechanics who can do the work. There's value there.
Neither engine makes these trucks into Porsches. If you feel like towing a 7000 pound trailer over mountain passes, maybe go with the 6.2 (or a 3/4 ton diesel pickup). If you must have the top available engine in any car you drive, go with the 6.2. Otherwise, think about the 5.3 - it's beyond fine and it's cheaper.
I recommend the 20" wheels. Better ride, cheaper tires, better curb protection, better pothole survival. Size looks fine - rolling radius is exactly the same as the 22" setup. Though, the GMC 20" wheels are much cooler looking than the Chevy ones. IMO.
Pricing is odd on these trucks, as the OP noticed. A Premier Tahoe or Denali Yukon can be $10K more than a well-optioned LT Tahoe or SLT Yukon, and in my own cross-shopping experience I did not see that much value differential. I believe you pay an awful lot for a high-tech suspension that will probably be expensive to maintain downstream, power running boards that don't seem necessary to me, and I know for sure the 22" wheel option adds over $2000.
I went with an LT Tahoe that had almost everything on it; seemed like the sweet spot to me. But some people have to have the top of the line, I get that.