Whenever I try and move up a slope or staircase, Garrett tends to slow to a complete halt unless I'm running, and frequently gets stuck on the top step and won't move into the next floor unless I approach exactly the right spot at exactly the right angle. Or jump, thus alerting every guard in the room.

Is this a known engine problem, or has something gone wrong on my end that I can fix? I've put up with it for most of the game, but I'm having real trouble just getting into one room in the Mage Towers level.

I remember having trouble with slopes, too, though not, perhaps, to the extent where it greatly hindered my progress. I'm not sure if it is a problem that can be fixed, however.

I'm aware that this happens, but it's a pain to fix (finding ALL stairs and making sure they are not too tall), so unless it's completely game breaking, I'm laving it alone.

Change the options concerning the how you attach to ladders; walk or jump. Generally, walking is easier. Also, make sure to move the mouse/camera accordingly, while trying to navigate a ladder. Move Garrett and your mouse exactly as you would move in real life (looking up while going up, looking down while going down). And you can even keep shift pressed to land with lowered noise.