I'm a little confused.
If you were concerned about weight, why did you wait four years to weigh your rig?
In those four years, how much "stuff" have you loaded into the trailer, how much does it weigh, and could that have contributed to your overweight issue?
The truck GVW that you mentioned, is that with or without the trailer hitched?
Even more confusing is the comment from "the wacko cat". What do the specs from his Dodge 3500 SWR have do do with the specs from your Ford dually? I can't make the connection.
At the end of the day, you are still reasonably close. We all know, or should know, to never just take a salesman's word for something, especially if your plunking down a bunch of money. Always verify before you buy.