Apples to oranges...
Jeeps are not road vehicles, though a lot of people run them that way. Trailblazers are not off-road vehicles -- same issue.
The Jeep JK is actually the best "dual purpose" vehicle built, quality issues aside (and I'm not convinced they are worse than similar year Chevys).
I can't speak for the JK, but the TJ I owned was far less capable than the two GMC products currently in my garage for one reason: open differential. Here we have a Wrangler "Sport," loaded with th 4.0L, air conditioning, and cruise control, but if the right wheels are in mud and the left wheels are on solid ground, you're going nowhere. Any vehicle which leaves the factory without a locking or limited slip differential has no business venturing off the pavement. I got that thing stuck one time and was forever reminded of just how badly--by the mud still trapped in the right corner light. I vowed never to be stuck again, and had an ARB air locker installed by Drivetrain Direct in Riverside, CA (and swapped the 3.07 gears with 4.10 at the same time). A Jeep with the right mods is a serious off-road vehicle, but unless it's a Rubicon, it's nothing better than any other 4x4 SUV--but the road manners are absolutely horrible. Compare that to my 04 Yukon XL SLT, which is as plush inside as any limo I've ridden in, and is as comfortable on the highway as on the beach. The Yukon is truly a dual purpose vehicle. I haven't taken the Envoy off road yet, but I'm guessing it's shortfall will be in ground clearance.
Back to the discussion of differentials, I know my Yukon has the Eaton locker. I don't really know how it works other than when one wheel slips is engages with a thump and I continue forward. How it senses that I have no idea. I just bought the 07 Envoy Denali, which I believe to have a limited slip and traction control. All the SLTs I saw on the lot had locking differentials listed on the sticker, which I'm guessing is the same Eaton unit in my Yukon. I didn't see any Denalis with "locking differential" listed; they all said "limited slip differential."
Where in the VIN are these codes you're deciphering? I'd like to know what gear ratio I have. It doesn't feel like a 3.73.