I've found out that increasing "10" into "100" in gravity code affected on stairs movement. Now player can't walk up on slopes, but movement on slopes is extremely smooth. I'm thinking on how to fix that (player can't walk up on even very small stairs). But if I leave it as a negative value (-10) and limit FPS at 60, then everything works perfect (smooth movement on slopes and stairs). About the TILT and ROLL angles of camera. I change camera's TILT for aiming up and down, plus I change ROLL angle for making an explosion effects. I don't change player's TILT and ROLL angles (that's why I tried to use "my.pan" for "vec_rotate" instead of "camera.pan"). I rotate it with player's PAN angle only cause I use blobbing camera effect (see this line: "vec_set(cam_pos.x, vector(0, 0, cam_height));", I use variables for Y and Z additional to cam_height). If I won't use that blobbing effect, I would remove "vec_rotate" cause as you said it's not necessary

Edit: By jerking I mean that camera's Z position moves up and down a little bit while moving down on slopes (fast). If I use "vec_set" without lerping everything works good.