I have this weird issue with my Sc400 (stock 1uzfe and auto tranny). When driving straight at mid to high speeds (60-80) I get this weird whobble effect. This isn't the normal bad wheel bearing whobble, but it feels like the rear end is sliding suddenly left or right. It isn't sliding far or anything, just centimeters left or right, but in the cabin of the car you feel like you're drifting for a second. The wheels are not breaking traction or anything, no noises are heard when this happens, and it only happens when going straight while going higher than 50mph. In corners the steering wheel has a slight bit of lag or play before the car starts the initial turn, but in the turn, it's completely solid. I need to replace the power steering pump as it leaks when it gets cold, and possibly the steering rack, but is that what's causing this problem? I'm not sure if the description of the issue will help or not. The best way I can describe it, is like if you are riding a motorcycle and lean to the left or right enough to feel off balance and then jerk it back to the other side to stay up, that's kind of what it feels like.