I just noticed a slight vibration when going at lower speeds between 2nd and 3rd gear. If I am accelerating at a decent speed the vibration is not there. I also noticed it going up a hill at a lower speed but as soon as I gave it more gas, the vibration went away. Anyone else notice this? 2007 GS350 AWD by the way.

 

Rear tire could be out of balance or could be a bad tire Im having a similar problem but it's cause I have a bad tire.

 

Drive shaft?

 

It could be something as simple as loose lug nuts, eliminate the most common and obvious causes.

 

In all honesty, i don't know if the GS even has a locking rear diff but if it does, it sounds a little like you may need some additive. My guess is that it doesn't have a true locker since it has trac control but it might anyway.