I calculate it this way:
6340-2840=3500lbs. This is your rear axle limit
3500-200=3300lbs. Subtract 200lbs for the hitch
12000 X 0.25=3000. Guesstimated pin weight if the 12,000lb trailer is loaded to the max
3300-3000=300. You have 300lb margin on your rear axle.
2011 Ford F-150 EcoBoost SuperCab Max Tow, 2084# Payload, 11,300# Tow,
Timbrens
2013 KZ Durango 2857