Thought since i was new here I'd point out some problems i have had with my truck. I was going on a trip in December and decided to have my fluids topped off at a local lube place since it was pretty cold out. They told me my rear end fluid was nasty and showed me a sample.

I really don't trust those places so i decided to go to a friends garage to check it out. The rear end vent hose is ran to a nipple on a bed cross member. The cross member is open on the end and allows dirt, water, and who knows what else to be funneled into the rear end. Next time your under your truck you may want to check out this line.

I unhooked mine from the cross member and mounted it up high. I put a upside down U in it so water can't get in.

Also check your fluid to make sure it hasen't been taking in water and crud.

I don't know if this has been covered before but i thought i'd throw it out there