what is towing capacity

In general Towing Capacity is the amount of weight your vehicle can safely tow and stop. You also have a rating for GCVWR (Gross Combined Vehicle Weight Rating) which is the total weight for tow and towed vehicle. You also have axle ratings which is the maximum amount of weight for each axle.

Is it Diesel? In general, the F350 can pull 12, 000 lb

Im buying 1990 350 ford. plan on putting a 40 ft flatbed and hauling freight. Im confident it can pull the trailer which is 8K and 10-15K lbs on top of that.