Towing a 18,000# trailer is 1 issue, the other is the 3,600# pin weight. GVWR is probably 9,200# (check drivers door column) truck probably weights 7,000# so 2,000#? payload.
Probably only has a 6,084# rear axle. GCWR is 22,000# (7,000 truck + 18,000# trailer = 25,000#)
Personally, I think you...