How to stop acceleration on slopes? (2D),How to stop acceleration on slopes 2D?

I'm trying to make a 2D autoscroll game where the player can only jump up and down, or get pushed by objects. I recently tried adding stairs with diagonal colliders (otherwise the player wouldn't be able to go up the stairs) but the player seems to accelerate when going down the stairs and decelerate when going up the stairs (up till the point where it stalls and falls back down the stairs). Thing is, I want the player to keep a constant speed.

I think part of the issue might be that I have a material applied to both the player and the stairs, which has very low friction, to prevent the player from getting stuck on objects when jumping or falling.

TLDR: Is there a way to make it so that the player has a constant speed, even on slopes?

Thanks in advance!