I think the point here is that it is a very steep grade reguardless of the math ........
I think the real point is that the OP was in error on the grade and has not come back with clarification.
He is probably still out there trying to measure it.
The one thing I would say is force it into low gear and put the RPM at the torque peak before you enter the hill. Don't let it shift automatically. You want to make sure the engine does not bog down, turn too slow and slip the trans excessively.
Being in that part of the country and I did see some inclines on some housing around Lake Hartwell. If it is anything like those homes, it is impossible to take a coach down an incline like that. They do look like thirty degree inclines.