helpful folks!
I just wanted to say thanks for the info posted here. This is by far the most informative auto forum I have found for my car.
Under scheduled service the toyota dealer has changed my trans fluid. As has a "shadetree" family mechanic and myself. Until I found the info about the differential in the FAQ I assumed it just used gear oil and was good to go

. Today I went and drained the trans pan and diff...the diff fluid was friggin BLACK and the end of the diff plug looked like it had JB weld on it from nearly 140k of use and abuse. After the change my 1-2nd thunk/lunge is gone and the thunk when I take my foot off the gas is gone too.
So again huge thanks for all the great info.