I can see the R/A bearings running a bit warmer, due to carrying more than 1/2 the load, but 30-40 degrees, seems excessive. Is your FW loaded to close to GVWR, and your rear axle maybe at RAWR or slightly over?
I have noticed bearings 10 degrees warmer, one side to the other, caused by sun, or more than normal slope of road.
I've noticed that a bearing set, that has been hand packed, will run 10 degrees cooler than the one next to it, that has the hub filled from EZ-lube use.
I will mention, before someone else does, it could be the new B&W hitch! :)
Jerry