I have the 6.0L cast iron block LQ4, with the 4L80e transmission and 4.10 gear ratios front and rear. The acceleration, top speed, and towing performance have all been very satisfactory bone stock, with no tunes, chips, CAI's, or exhaust modifications. The critical final gear... the tire size, where the rubber meets the road... is bone stock as well.
The LQ4 was built without any of the displacement on demand stuff that I hear folks complain about. My towing experience with this drivetrain has been with trailer weights as high as 7,500 lbs at elevations as high as 7,500 feet. However, towing is not as frequent as simply running loaded with the back full of about 600-700 lbs of gear.
The 4.10 gears take full advantage of the 4 speed heavy duty 4L80e, in that each gear in the transmission is more fully utilized when accelerating from a stop, when passing mid speed, and when going up hill. This vehicle easily and comfortablly cruises at 30 over. (You do the math, and observe that I did not say that "I drive" the vehicle at that speed).
If I had a 5.3 and was considering doing a swap, I guess I would be curious about the 6.2 only because it sounds slightly larger... but if it has any engine computer to chassis network integration issues, DOD programming that kicks in when you least want or expect it, or thinner cylinder walls in an aluminum block, then I would question if that mere 2 tenths of a liter is worth the trouble. Know that the 6.0L LQ4 is a very capable, durable, proven, and popular block in 3/4, 1 ton, and even box trucks in the Isuzu line, so availability and access to parts and programs will likely endure for some time to come, just like the ubiquitous small block Chevy 350 has for the last few decades.