I'm going to second the above. I catch hell for saying it occasionally, but stay inside the manufacturers GCWR. Will the truck pull more? Yes. Will it pull more and still have a respectable safety margin? No. Also get a good brake controller if you do not have one.

Kwikkordead: "I fried the brakes on my '95 F-250 with a 14,000 lb trailer. Instant warped rotors." Did you have a brake controller? If so, how was it set?