Let's recap, because I think we've lost track of your story.
In your original post, you said you made a range downshift? It's fairly safe to assume that was at the top of the grade, since range shifts generally happen at <25mph. You said in another post the transmission malfunctioned.
So the tranny failed to range shift at a fairly low speed, but the truck accelerated to 70 mph before you realized you had a problem. So the whole time the truck is accelerating you didn't realize there was no engine or Jake noise. And the brakes were hot when you realized there was an issue, which means you'd already been on them while the truck was accelerating.
"Does not compute"
I really don't even need to go further than that. And yet here you are telling us that WE don't know what we're talking about? I mean if that's not correct please give us a step by step of what happened, so our inferior intellects can grasp what happened