The weight of the truck or the trailer means very little. It is the Gross Combined Vehicle Weight that the DOT looks at when inspecting the truck.
My 2007 GMC is rated for 11,400 gross weight. My trailer is de-rated to 14,500 pounds. Thus the GCVW is 25,900 pounds. The empty weight is approximately 15,000. Thus pay load is 11,001 pounds. Any combination over 26,001 will require a CDL according to the Fed guidelines. Any actual weight over 26,001 pounds may result in a fine.
In addition the weight on each axle must been under the rating on the spec sheet.
For example my trailer has 7000 pound axles. If the load of 8000 pounds is placed on the trailer to far to the rear and the trailer axles weigh more then 14,000 pounds I would be overweight and subject to a fine. If the load is placed to far forward the rear axle of the truck could be overloaded.
You also need to check the weight capacity of the tires and not overload them either.