Yes, it looks like you have a 5,000 lb hitch as well.
I just had my RV and toad/dolly weighed at a CAT scale and the car/dolly weighed in at 4,040 lbs. My GCWR - GVWR = 4,000 lbs with a 5,000 lb hitch. I'm about 700 lbs below GCWR so I'm a bit closer than you will be.
80% of the rating is something I'm comfortable with. Just remember to factor in the weight of fuel and junk you may decide to carry in the Acadia.
If your Adventurer is close to 18,000 lbs with its stuff, be aware that you're increasing the total weight by over 20%. Be certain to get a toad braking system installed.
2020 Forest River Georgetown GT5 34H5