Sounds like a fun outing :) I'm jealous as the biggest thing my 6.4 Hemi has hauled in the last couple months is a Christmas tree.
My TT is very similar weight and here in Oregon I'm familiar with the steep winding roads you talk of. Coming from a diesel I'm very happy with this truck. But, my only area of displeasure comes in the steep winding terrain where the gap between 1st and 2nd gear seems like a mile. I find myself spinning at 4500 RPM in 1st or lugggggggging at 1400 RPM in second to maintain a typical curvy road speed of say 30 MPH.
I have the 3.73 gears and would MUCH rather have had the 4.10s but didn't want to pay/wait to order so I took what I could get on the dealer's lot.
Anyway, just curious what ratio you're running and what your take is on the low speed hill/curves with that load.
Again, I love my truck 98% of the time so Ford fanboy trolls please refrain. I'm talking about pretty isolated set of circumstances that are less than ideal.