Here is the good news!
My 2006 36FDDS total loaded vehicle weight is 27000#
Pulling a 7% grade for 10 miles @ 65 mph resulted in a maximum coolant temp of 200 degrees that immediately went down when the grade decreased.
Normal running on the flat gave ~180 degrees
Brad at Macs Radiator said that in order to compensate for the differences in heat dissipation between aluminum and brass, they added more tubes to their radiator design. I can attest that the new radiator worked as good, if not better than the old one. The crucial test will occur later this Summer when the ambient temps in So. Cal. hit the 80's and 90's. I have confidence in the new design and materials
2006 36 FDDS
Cool and Good to Go!