How to increase towing capacity?
 

Im gonna be towing a 28ft horsetrailer gooseneck this up coming spring for livestock, and wanted to know what can i do to increase the towing capacity?? I have a 89 F250 5.8 with a C6 trans and 3.55 gears. Trailer ill be towing weighs 11,500 lbs. Most ive towed with my truck is 9500

That's gonna be heavy with that truck. You could get 4.10 gears, but with a C6 it won't like highway speeds. A transmission cooler would help.

Get a bigger truck. You're way over GVWR and GCWR for that truck, and that's when the truck was new--never mind over 20 years of beating around on the roads developing metal fatigue in the frame and suspension.

Jason

Second the 'get a bigger truck' - not only is the chassis and drivetrain not legally rated to tow anywhere near that much, more importantly the brakes aren't either. Which can lead to fatalities when you burn out the brakes trying to stop something that heavy.

You're into 1-ton diesel territory there, no question about it. The truck may move it, but everything will be working to its limits and the chance of failure (engine, trans, cooling system, etc) will increase significantly. As mentioned, a trans cooler if you don't already have one is always a wise investment. 3.55 gears are far from ideal for heavy pulling, youll be putting your foot to the floor on hills and starting from a dead stop.

I would actually move towards an F-superduty at that weight.