Several posts here about mysterious failures of rear axle seals. My experience: Had a local mech try to adjust parking brake. He could not, put truck on lift, found some strange lubricant on the parking brake shoes - diff oil as it turned out. Took it to dealer who found that air vent on diff housing was blocked, blowing out the seals and destroying bearings. Fixed under extended warranty (2007 OR). From the other cases with similar effects, suspect the air vent in diff is prone to blockage.

That is why people take off the air admittance valve and extend the breathers. Both front and rear, and the breather for the tranny.

Thanks Granitex but you could please explain that.. what is the part and where does one get it? Is this usually done for offroad use?

Depending on the model that you have, there is one of two types of breathers. The most common is an air admittance valve. If you look at your rear axle and see a stubby little tube with a cap on it you have an air admittance. If you have a rubber tube that goes from the same spot on the axle to the underside of the body you have the other type.

Assuming that you have the first, you have two options:
1 replace the entire valve, with a fitting that has threads on one end and a hose barb on the other(I forget the part #)
2 Rip the cap off of the air valve and put a piece of fuel line over the exposed end and tighten down a small hose clamp.

Then run the hose to a location that is higher than what you think that you will go. I ran mine into the drivers side tail light assembly. You will need to drill a small hole to run the line into the tail light.

The front diff is extended to the top of the tranny hump, beside the tranny breather. You can not see them but they are there if you stick your hand down there.

It is done so that you do not suck water into your diff, or tranny when you get into deeper water(which water in your tranny is really pricy)

Air expands as it gets warm, and contracts as it gets cold, and you need a way for that to happen or you will blow seals, or suck in water.