I cracked open my front diff last night to change fluid, what a mess. The fluid is a greyish-black and it is full a shiny silt, I'm guessing this is metal shavings. No kidding I wiped my finger in the bottom of the case and it turned silver. No metal chunks or anything, just a fine metal silt.

What should I use to clean this out? PB blaster or WD-40? I'm worried about using anything too harsh, might create a problem with the new fluid. I am putting amsoil 75w110 back in just need to clean it up first.

Is this something I should be worried about or is this normal for a 50K mile truck that's never had the diff serviced? I know, I know...

There also is a tube connected to the fron diff is this a vent or what?

By the way the rearend diff fluid looked fine hardly any smegma at all.

Any thoughts?

Use brake cleaner to clean it out! That is just the normal for 50k. That is just a vent tube. The biggest differance between the rear and front is that the front diffs use a lighter weight than the rear does. Most because the front diff is not the main one for driving and the heat from the engine.