AS2 Uphill issues

[Degraiver]

As the title says, I have an object moving downhil just fine but instead of moving uphill it will move through the hill.

How do I make it move along the uphill slope?

onClipEvent (load) {
	grav = 0;
	spd = 1;
}
onClipEvent (enterFrame) {
	if (_root.ground.hitTest(this._x, this._y, true)) {
		grav = 0;
		this._x += spd;
	} else {
		
		grav += 0.3;
		if (grav>5) {
			grav = 5;
		}
	}
	this._y += grav;
}

Edit: So it wont let me upload an attachment so ima try this
-O-----O <--- there are 2 balls here, gravity makes them fall hitting the downslope.
\........../ They slide down normally and move to the other side.
\\____ // Where the Uphill for each begins. They will pass through the uphill like it was a flat surface. I hope this helps explain what i mean.
If not please ask for more description.