This is an excessive toe (factory spec) issue. Nothing a rotation will fix.
Tell your alignment shop you want it set to 0 for the toe. ZERO TOE.
All you four wheeler guys telling him tire rotation, that is not the answer. Breaking down 6 tires to do a conventional tire rotation is a waste of time & money on a dually and is completely unnecessary as long as the alignment is set right. Doing a rotation in this case is a band-aid and still promotes unnecessary tire wear. Fix the problem and get the alignment with toe set straight to 0.
that's the same wear I have on mine after 28,000. the R/F one worn a lot on the outer 2". when I had it in for a recall last month the service notes suggested front end alignment needed. this must be a factory setup issue as lots of owners are getting the same kind of wear on the R/F tire.