Unrelated to OP’s issue that is now fixed but I had similar issues running different brand tires in the fronts compared to the rears, car would ‘float’ anything above 50 mph and felt unbelievably unstable as the tread patterns of different tires would give different feedback on the road front to back

 

Thanks lobux, do you happen to know the torque spec for the ISF's alignment bolts for the front and rear? Seems like mine has gone out of whack slightly after 6 months from the previous alignment, which leads me to believe the alignment shop isn't tightening to spec....

 

Rear Eccentric bolt: 50 N·m (510 kgf·cm, 37 ft·lbf)

There are no adjustment bolts/nuts in the front except the tie rods, and IME those are not torque critical. Two gorilla grunts is plenty, but if you have the right tools, the manual says 56 N·m {571 kgf·cm, 41ft·lbf}.

 

Funny I saw this post - I just started driving back into the office and noticed that on the highway (60-80mph) lane changes or quick adjustments of the wheel make the car float in the lane.

I'm going to put new shocks/springs on the car and have it taken to Lexus to do a once over.

Its either the car is riding on blown shocks or bushings are worn out.....car has 74k on it.

 

Or your tires are not inflated correctly, or have damage, or...

My shocks and springs had over 200k on them when I put the Ohlins DFVs on it. I'm sure the OEM units were well worn, but I never had stability issues even with those old things on my car. I'd suspect tires and alignment before spending any money on hard parts.

 

I agree - I just had new Michelin PS4S put on it, and had an alignment as well.

Im throwing new suspension on it as the OEM 08 has really gotten to me as I get older, as well as having the folks at Lexus take a peek over all the bushings,etc on the car.