Dillon, the front brakes will be taking the brunt of the load during any downhill runs. Off road, I just drop it into 1st and use the brakes to help when engine braking is insufficient alone. Brakes and first gear will do well if the traction is decent. If traction is poor, you need to be really careful with your brake technique.
The transmission seems to do well with long runs in low gears. I've spent hours in first and second gear at the Oceano Dunes. I was constantly spinning my tires, doing donuts, powerslides, slaloms, climbing dunes, and performing other dune hooning maneuvers. No sign of overheating the transmission.
On long highway downhill runs I just slowly apply, then slowly lift the brakes to control speed without risking warping the front rotors or over heating the brakes.
Also, on highway hills and mountains I turn off overdrive. This not only keeps it out of the top gear, but also seems to run a sightly different shifting program more suitable to inclines.
Cheers