What is the towing capacity for my Ford truck?

I just bought a 1989 Ford F-350 dually. It is a regular cab, has a 460 gas engine, an automatic transmission. Can anyone tell me what the towing capacity is?What is the towing capacity for my Ford truck?call the dealer ship its all about what tires you have, a 10 ply tire can take a lot more load than a six ply, so check out the tire pliy rating, check with the dealer, (it may have a sticker on the door) on the drivers side, if its not pained overWhat is the towing capacity for my Ford truck?any idea on rear diff gearing? im guessing around 10,000 pounds might be more depending on if it has towing package/the gearsWhat is the towing capacity for my Ford truck?8000LBS OR 15000