It says total trailer weight including load should be never more than 3900lbs.
Does the narrative in the manual state the 3900 pound figure directly?
The .pdf has a block in the upper right corner that states:
"3500 LB MAX GROSS TRAILER WT
300 LB MAX TONGUE WT
DO NOT EXCEED TOWING VEHICLE RATINGS"
I hope you are NOT adding 3500 and 300 together.
It looks to me that 3500 Lbs is the absolute maximum allowed by this hitch. The 300 Lb maximum [b]tongue weight
should be subtracted
from that, to figure there should be no more than 3200 Lb [b]axle weight