I had/have an 03 Tahoe LT, with essentially the same set up as your Yukon, except being 4wd. Here's some observations and things that might be helpful.
If possible, take your Yukon and the Lance trailer you want to buy and take it to a scale to be weighed. Do several passes. 1 - the Yukon solo. 2 - The Yukon with the trailer hitched. 3 - The tongue of the trailer. Gives you all the exact, significant weights you'll need.
The owners manual recommendation for GCWR for my set up was 14400. The real world weight of both was 11780 at the scale, with all of my stuff, 50gal of water and 2 full fuel tanks. Trailer weight alone was just shy of 6000lbs.
If you don't need the 3rd row of seats in your Yukon, remove them. That's the first thing I did, since unnecessary. A bit of payload increase.
The slightly longer wheelbase on your Yukon should be an advantage. With my Tahoe and Outback combo, there was a LOT of porpoising on many roads, frequently on interstates. Not a pleasant sensation for miles and miles on end. I also have a WDH, and sway was rarely a factor, usually only when being passed by a semi or bigger MH.
Whenever possible, travel with no water on board. There may be times it is necessary however. I go to a lot of USFS CG here in Colorado, though they have common water, sometimes they do not have threaded faucets. Get one of those water coupler thingies from Amazon. Also, most of these USFS CG don't have dump stations so you'll need to haul gray/black water to a place to dump.
Recognise that you will not be going fast in the mountains. With my set up, and a lot of 7-12% grades, I would be lucky to be at 30mph. Put the flashers on, whenever possible, drive along the shoulder to let others pass on those 2 lane roads. and just don't stress about it.
Your fuel mileage WILL SUCK. That is a fact. Towing on the flats, I would get about 9-10mpg. In the mountains, 6-8mpg. With a 26 gallon tank, I would start looking for gas with 150 miles on the trip odometer. On the flats across eastern Colorado, Nebraska, or Kansas, I could get about 200 miles on a tank. In the mountains, I'd start looking at 100-120 miles, and top up frequently. Fuel stops are going to be few and far between in many mountain locations. One place I like to go, the closest fuel is about 50 miles in any direction. Get a good gas app and check it prior to travel for the day, to find good fuel locations along the way.
If you plan your trip to the PNW using interstates, this likely would not be as much of a problem. However, if you plan on using secondary roads, where towns and fuel stops could be signicantly far apart, then fuel stop planning becomes a necessity.
While I still have the Tahoe, as it is an excellent vehicle, I replaced it with a '07 GMC Sierra SLE (classic) 3500HD. Same trailer. A bit of overkill some would say. But I bought it prior to a trip to SW Colorado, the 4 corners region, and on to both rims of the Grand Canyon. I wanted something that would tow across vast stretches of highways and not have to constantly try to figure out where to get fuel. With my current set up of the diesel and the Outback, I get consistently 11-13mpg, whether on high elevation flats of northern Arizona or towing up and over Wolf Creek Pass.
Still love the Tahoe. Love the Sierra more for towing, though.
2007 GMC Sierra SLE 3500HD Dually
2016 Coachmen Catalina Legacy Edition 243RBS
2007 Keystone Outback 25RSS - R.I.P.