RE: Drew: How about a DIY on the rear Diff??
thediff fluids can be changed 1 of 2 ways, pump it out or pull the diff cover.
if you pull the cover,
1) Put oil catch pan under the diff housing
2) Untorque all of the diff bolts and loosen them so that oil can escape from the diff
3) drain diff until most of it has been removed, then remove the cover
4) clean the mating surfaces really well so there is no silicon sealant on it and the housing.
5) make sure both surfaces are free of oil and are clean and dry.
6) wipe out the bottom of the diff housing to get any gunk out that may be there.
7) apply sealant(black or orange silicone gasket maker works fine)to the diff cover, replace the cover and hand tighten all the bolts back into the housing.
8) using a torque wrench tighten every other bolt to 30 ft lbs of torque until all of them are tight. I would recommend doing it in a couple of steps, maybe 15 lbs all the way around, then the 30 ft lbs.
9)pop out the fill plug (rubber) andrefill with your favorite 75w-90 fluid (amsoil or redline are good choices... also mobil 1) or if your towing heavy, use a heavier oil. the shop manual specs 75w-90
I recommend using a pump to fill the diff, makes it easier than trying to pour fluid in.
I also would recommend gettinga marine oil change pump to vacuum out the diffs if you dont want to pull the covers.
Hope this helps...