Hi,
I would separate the problem in two.
can you position dummy cubes under the feet of the character on the slope, do that with first some simple dummies, then plug the character feet. make sure the cubes are position and rotated properly to match the slope.
once you have that, I am not even sure how you can force an animation to adjust its feet placement to match the dummies you have now in place.
let me know when you get the first step, this should require only one raycast per feet, straight down and the first hit is your slope, get the hit normal and position and match the cube transform to that.
Bye,
Jean