Tow Vehicle for 3500 lb gvwr travel trailer

Thanks everyone for your replies, I'm beginning to feel a little more educated. In regards to the GCWR. My understanding is that is the total amount of weight between the tt and tv. To determine GCWR do I add the tv GVWR + tt GVWR (6400 + 3500= 9900) or would I add the tv curb weight + tt dry weight 2623 (4646 + 2623= 7269?

Either way I'm not sure I understand how this number comes into play if the tt GVWR + tv loaded weight = about 1000 lbs below the towing capacity of the vehicle.

Thanks again!