Y2KGUII ZD Wgn
Agree.Have you fitted a torque converter lock up switch, should help with engine braking. Back in the 70's we frequently did that road towing similar weight van in an Austin 1800. Never had problems with brakes going down, but always overheated going back home.
As for brakes, quality rotors with EBC Yellow Stuff pads are highly regarded or front pads from 4.8 GU.
I have the 4.8 front 'soft' pads against my RDA dimpled and slotted, works bloody great and very little dust, unlike other 'soft' pads.