Max towing is GCWR minus the curb weight of the truck. Keep in mind that anything you put in the truck also subtracts from your max towing, you, the weight of your hitch, your lunch, etc. etc.
You're probably better off starting a thread with all the specs of your truck, what you intend to use the trailer for, if you have a CDL etc... You're likely to get better answers that way than just hijacking another thread.
You can also put truck specs in your signature so it'll always be there, even if it's just the basics i.e. 2500/3500, 6.4/6.7, SRW/DRW.....