Welcome and I'm sure you'll get some answers on the axles...seems to me they were using 4,400# but someone else with the same model can address that for you. You will find some very helpful people here and if they can't answer you they will tell you where to get your answers.
Jim & Linda Tator
2013 Crusier CF34SS GMC 3500 8.1L Dually
154 nights in 2013 - 4,370 miles
178 nights in 2014 - 5,082 miles
365 nights in 2015 - 6,040 miles