Auction price will depend on the condition of the truck and the cost of repairs.
Look at the KBB of your truck, subtract 20% for the rebuilt title. That's where whoever buys it will place it's "completed ready" for sale value.
Now as to what it will bring at auction, start subtracting stuff.
Auction / title fees will be $500.00 ish.
Transport fees 500 to 700 ish.
Make a list of parts you can see it will need, put a value on the cost of those parts, then double it.
Repair labor cost is tougher, because most of the guys buying these don't pay shop rates. They have their own shop and use these as fill in work. Rule of thumb is take your estimated parts cost, and use 75% of that for "builder labor" cost.
Stolen and recovery trucks are a bit harder to estimate than a collision repair. If I'm looking at a recovered truck, I'm looking for severe abuse, (think aggressive off roading etc etc) and then anything they took off of the truck. The obvious things are wheels and tires / stereos / you get the picture. Then there is the manner in which the removed the parts. Think "smash and grab". They cut wires, bust plastic, drop it on the ground after they take the wheels and tires. So busted rotors, etc etc etc.
Add all that up, subtract it from the KBB minus 20% and that's where most guys will see their high bid.
Keep in mind this is all a guess. There is always the chance of some wildcard, that just has to have that truck, and drives the bid up. But you have to start somewhere.
Check places like 74Auto, look at what they are asking for similar builder trucks. They buy them at auction, then mark them up $1,500 ish and sell to the public.
Builder Duramax trucks usually are at a higher demand, plus its a Denali. There will be bids, for sure.
https://www.74auto.com/trucks.php