[whiterose]

I have a similar vehicle to yours, mine is a 2015 Denali with Duramax and Allison. I have had my truck on the CAT scale, full tank of fuel, 5th wheel and heavy duty bed cover. Front axle = 4580lb, rear 3360lb. GM axle max is front 5200lb, rear 6200lb, but with a total combined of 10,000lb.
Say your driver, passenger and cargo comes to 400lb, you can assume equally split between front and rear. IE 4780lb front and 3560 rear. The rear axle is capable of a pin weight of 6200 - 3560 = 2660lb. However, should you load to this amount you have exceeded GM's combined weight by (4780 + 6200 - 10000) = 980lb
In your case you will be close to 4780lb front and 5830lb (3560+2270)rear for a total of 10610lb. Within axle loading, but high on the combined.
You need to get your rig on the scale. Now that I have taken delivery of may new trailer it will be on the scale before my first trip.
The year of your truck can also be a factor, between 2015 and 2016 GM significantly reduced the 5th wheel towing capacity. I suspect there was no change to the truck, but possibly conformance to the SAE or some other national standard.