Long-time reader, very rare poster...
I have a similar situation on my driveway. 1/4 mile through the woods, up a hill, with one part that is approaching about 8% grade. The wheel ruts tend to catch water and cause erosion problems instead of flowing into the swale. Driveway is built of crushed gravel, and is topped with recycled asphalt (reground, with whatever other junk falls in). My biggest issue with it is I am losing fines, leaving just stone (which is generally round-edged in recycled asphalt around here).
Any thoughts for how to keep the thing "happy"? If I grade it and then it rains before it repacks, it washes out. Have dreams of taking a 2x5 foot tank I have and making it into a roller, and then putting a vibration motor on it, but I have plenty of other projects ahead of it in line.