OK.. so here's my take.
You say your cargo capacity is 1400(ish). You are at that, or over. 980 tongue weight, 100lbs for the hitch itself. 400lbs for family.
I had a 2011 GMC Sierra 1500, cargo capacity of 1600(ish), a 26 ft trailer, weight loaded about 6800 lbs. That was all I wanted to tow. No way I would have done a 8200 lb trailer
Im not familiar with the scale you used, so, question. When you say trailer weight of 8200, is that supposedly including the tongue weight, or is it basically the axles on the scale. Because, if it is the axles on the scale, and does not include tongue weight you are looking at 9180 total trailer weight, and a tongue weight of 980 which is just a skosh north of 10 percent. So, that will create a situation where you will be prone to sway.
I still think you have too much trailer for that truck. But, you could try to re do the hitch. Follow the instructions for setting up the Blue Ox. Take measurements of wheel wells from ground up with no trailer hooked up. Then same measurements with trailer hooked up. Objective is to get the WD hitch setup so the height of the wheel wells when the trailer is hooked up, is the same as truck standing alone (or within 1/4" I think).
That's a lot of trailer... that's along the lines of what Im pulling with my 3/4 ton. No way on this earth I would try it with a 1/2 ton.
Mike