Given ,
wrote:

Rerally nothing of you don't need synthetic. All you NEED is a simple
GL4 gear oil like the Walmart LubKing GL4. Synthetic doesn't thicken
as much in the cold, or thin as much in the heat, and MAY last a
little longer, but not enoughlonger to make it worth 4 times as much
(there isGL4 oil available for as little as about US$16 a gallon)

I was hoping to get good information like that so I thank you because all
the guys on the Toyota forum are saying to only use Amsoil or Redline but
they don't really know why.

I'm looking at GL4 and SAE 75W90 as those are the specs from Toyota.

My one question to you is if the synthetic doesn't thicken as much in the
cold, how does it keep the 75W and if it doesn't thin out in the heat as
much, how does it keep the 90 rating?

Isn't that what the rating is all about?
So doesn't one 75W90 act the same at cold/hot as another 75W90?