I am in the process of changing out an axle on my 2010 Rockwood right now. It has a GVWR of 8,418#. The old axle was made by AL-KO, which has been acquired by Dexter fairly recently. dexter shipped me an axle with a different part number and a 3,500# rating instead of 4,000# rating, at least according to the packing slip. After numerous calls to both Forest River and Dexter, I am now pretty well convinced that Dexter has shipped the correct replacement axle. They have changed part numbers with the acquisition by Dexter, and the correct load capacity is 4,000#. It was a flat out error on the packing slip. Anyway, check your axle when it comes in.
I should add that the contacts at both Forest River and Dexter seemed to be knowledgeable and professional in trying to determine if I had the correct axle. Forest River has the capability to determine the exact parts used on your specific trailer if you provide them your trailer VIN.