Totalled, schmotalled... that'll buff right out! (kidding, obviously)
As the others have said... glad no one was hurt. Man, I can imagine the noise that made.
They probably asked you, but if you had just splurged for new tires, etc., you can have that accounted for. I had a car stolen once, and got a little extra $ b/c I had just put new tires on it.
I'm sure they asked about the mileage, so that's been taken into account. Higher mileage will subtract a lot; lower adds hardly anything (which sucks).
Make *sure* they know it's a Denali trim, just in case they didn't have it listed. These days, when they get the VIN of a vehicle in order to quote a policy, the trim level usually shows up, tho.
You can sometimes ask for another adjuster to assess the settlement amount, especially if they are allowed input for the intangibles that we all mentioned above. Otherwise, it's a numbers game, and their computer & NADA have the final say.
If all else fails, grab anything you think you can sell, off the truck. Like those wheels (but you'll have to put something on in exchange), the opposite running board-?, head / tail lights, anything you can get into the truck and safely get (the Denali steering wheel will bring some $, for example) In the shape that's in, I doubt whomever they sell it to is going to try and salvage much of the interior, TBH. And that affects the insurance company's offer, too - because part of their offer is based on what they expect to recover by selling it for salvage - which won't be much, given the condition.
Finally, if they have the option for you to buy it back, *and* you have the means to do it, the engine and trans would be worth a couple thousand; engine alone $1200-1500, depending on mileage, as it's an all-aluminum 5.3L LS (although the 823 heads aren't highly valued.) The rear axle wouldn't fetch too much, as it's probably a high ratio (3.23 or similar); GM stopped putting the 3.73 in with the V8 Envoys after '04.
Good luck on reaching a fair settlement. Fingers crossed.