With the 2021 the max trailering package isn't necessary to tow since the axle ratio is 3.23 for all options. It increases the GCWR by 500 lbs (probably related to the extra cooling) for the V8 options and add some other features like trailer tire pressure monitoring. For the diesel doesn't affect rating at all. If you plan to tow regularly it's definitely worth getting (especially with the V8), but if you're forced to get a truck without one you can make it work as the axle ratio was the most important factor that affected previous year models.
HOWEVER!!! With a family of 6 your limitation will be the payload of the vehicle, not the maximum GCWR. In order to tow safely, you need the be below the GVWR ratings of your vehicle, and below the GCWR combined weight. For the travel trailer, 10-15% of the trailer will be on the tongue of the vehicle. We're also a family of 6, and I did careful math before selecting the travel trailer to tow.
Here's an example for you, that will be for a 4x4 XL model
Estimated curb weight: 6,000 lbs.
Maximum GVWR: 7,700 lbs.
Maximum GCWR: 14,000 lbs.
Maximum payload = GVWR - curb weight = 1,700 lbs. (this is stamped on the truck when you get it)
Let's say all 6 of you are 150 lbs each = 900 lbs.
Then add some stuff in the Yukon = 100 lbs.
That leaves 700 lbs for trailer tongue weight.
This will depend on the travel trailer, but a 13% tongue weight is pretty reasonable to assume. Then the maximum trailer weight you could safety tow (loaded with your stuff, but probably with no water) is 700/0.13 = 5,384 lbs. Assuming you have about 1,000 lbs of stuff in the trailer (dishes, clothing, tools, etc.) then the trailer itself dry weight should be about 4,384 lbs.
This gets you exactly to the GVWR. Now to check the GCWR, total weight is 6,000+900+100+5,384=12,384. This is well below the 14,000 lbs rating, so it's fine here.
Make sure you do the math for you situation. The payload weight (passengers + stuff) before adding trailer tongue weight is the biggest determining factor for what you'll be able to tow. If you're unsure, definitely drive through a weight scale and learn how to find out if you've over or under the ratings.
Note that the advertised tow ratings are unrealistic for a normal family situation since they assume no additional payload inside the vehicle other than 2 people:
https://www.gmfleetorderguide.com/N...eID=21914§ion=trailer_specs&page=&butID=8
https://www.gmfleetorderguide.com/N...eID=21942§ion=trailer_specs&page=&butID=8