I do not think a weight distributing hitch will change the max tongue weight rating of the truck. It just helps lever some weight (force) on the front tires. There is still the same weight pushing down on the hitch itself. I have a WD hitch with 1K bars and I personally do not think the hitch even transfers 10% of that to the front tires. This is just my observation when I set the tension on the bars and see the reaction of the front suspension, or lack of. Trust me on this and look for a wet loaded trailer with a total weight of <#8000, you will be much happier and your Armada will thank you. Towing over #8000 is a tremendous strain on the TV, even with the Armada's power. #9100 is for flat straight roads with no wind. The Armada is a fantastic 1/2 ton TV, but it is still a 1/2 ton.
I for one think that the 1/2 ton rating is rather low. I personally loaded 3000 lbs of blocks in the back of my Titan and hauled it over 50 miles. Sure the back end sat down low but I had no problems whatsoever hauling this. I even have pictures of this load on my truck. Yeh thats my big butt holding the block. LOL