Regarding the rear differential breather, I realized I forgot to put the rear diff drain plug gasket on. As I removed the filler bolt I could hear air pressure being relieved from the diff, and this was just after replacing the fluid and doing a short drive. I thought the breather relieved pressure, or does it just "blow off" pressure at a certain level?

I'm not sure if the diff breather keeps pressure at a constant 1 to 1 w/ the atmoshpere or is there always an amount of pressure inside the diff.

While were at it, what are some recommended replacements for the stock breather?

 

Don't know about the pressure. Here is a parts source.

http://www.sonoransteel.com/Diff_Breather_Parts.pdf

These are Toyota parts so obviously you can source them yourself at the dealer. Being slow on the uptake I didn't quite get it at first that the top two are the actual breathers and the rest are barbs to accept the hose. Get the barbed breather and the 3/8 nipple. Some 5/16 hose and clamps and your set.

 

Thanks..my stock breather doesn't have a hose to anywhere, it just has a breather on top of the differential. I don't need to relocate it, I never drive it through mud or water. (Can't stand cleaning it up afterwards, and there's no place where you could get away with it and still tread lightly.)