Try using a gravel stabiliser! I used one on my driveway (which, which was also on a slope.. pain in the a***!)
The one I used was called COREgravel coredriveCoredrive, and it has really helped. It's from the UK, but you can probably find something similar wherever you live.
I saw this otheranother forum which was saying howsaid these grids must have a weed membrane already attached-, so when iI was hunting for a grid coregravel popped up a lot.., and iI must say the weed membrane is helping a lot.
While we were doing the drive we also did a couple paths leading to the house, which this grid could also help with!! Bonus!
plus it only cost me £11m2 (IdIt was very inexpensive, but I'd check the current prices, this was a year or so ago) for yourself.