I would take the less steep downhill route even though it may be long. The 7.3 diesel will not hold you back much at all without an aftermarket exhaust brake so you need to start at the top of the grade very slowly in a low gear and use your truck and trailer brakes off and on to keep the speed slow. Don't let it build up on you.
I had a Ford 7.3 for years (2002 - 2016) and it was a great motor for reliability but not so much for power compared to newer motors. I also added an exhaust brake for a couple of years but it failed twice so I disconnected it and never had a problem descending grades as long as I did as described above.
Barney