I have a 2006 F150 4x4 Crewcab. and 18 inch wheels and truck came
E with a trailer package. I added a manual braking switch under dash.

Can I tow a double horse trailer ?
Trailer is about 6500 Lb.
Both horses are about 2400 lb.
Weight of passengers and supplies is 600 lbs

Am I good to go ?

 

That would probably put you well over gross. Livestock hauling is for 3/4 ton and bigger trucks.