My usggest is that you read your owner's guide. It will tell
you what specifications the oils should meet. Be careful of
some of the Amsoil engine oils. Some are API certified and
some are not. Your owner's guide is going to specifiy that
the engine oil be API certified.

Here are recommendations for the other fluids from the GM
manual -

Automatic Transmission - DEXRON III Automatic Transmission
Fluid

Front Axle - SAE 80W-90 Lubricant (GM P/N 1052271, Canadian
P/N 10950849 or equivalent).

Front and Rear Axle (5 Spd.) - SAE 75W-90 Synthetic Axle
lubricant (GM Part No. 12378261, Canadian Part No. 10953455)
or equivalent meeting GM specification 9986115

Rear Axle (With QS4 Axle only) - SAE 75W-90 Synthetic Axle
Lubricant (GM Part No. 12378557, Canadian Part No. 88901362)
or equivalent.

Transfer Case - NVG 149-NP (One Speed Automatic) - DEXRON
III Automatic Transmission Fluid (GM P/N 12346143, Canada
P/N 10952622) or equivalent.

Transfer Case - NVG 236/246-NP8 (Two Speed Automatic) -
Auto-Trac II Fluid (GM Part No. 12378508, Canada Part No.
10953626) or equivalent.

Transfer Case - NVG 261-NP2 (Two Speed Manual) - DEXRON III
Automatic Transmission Fluid (GM P/N 12346143, Canada P/N
10952622) or equivalent.

Transfer Case - NVG 263-NP1 (Selectable) - DEXRON III
Automatic Transmission Fluid (GM P/N 12346143, Canada P/N
10952622) or equivalent.

Using synthetic fluids is fine, just make sure they reflect
the appropriate GM specifications.

Ed

If the Amsoil is API approved, go for it. If not, kiss your warranty
good-bye! Use Lucas oils instead.

2003 silverado, 4wd, 6.0 liter engine, 4:10 rears. I would appreciate
your comments on using Amsoil as motor oil. And using synthetic oils in
the transmission and differentials. I don't know which oils to use in
the transmission and differentials suggestions would be appreciated.
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Howdy Dave, there's nothing wrong with any of the Amsoil Engine Oils,
other than thier high price. If you are still considering changing Oil
at the Manufacturer recommended intervals, perhaps just go with Mobil 1
instead, and save yourself a few bucks along the way?  I've been using
Mobil 1 on my '97 Tahoe since new.

Wally World sells Mobil 1 in 5qt Jugs, and usually sells for $20 a jug.
(not sure how many quarts your engine takes?)

As far as transmission fluids go, I assume your truck has a tranny
cooler from the factory, so this is good.  

Amsoil does make a full synthetic Transmission fluid, again not cheap,
and I have this in my Tahoe, and it works fine.

If you are going to do the Transmission Service yourself, I'd make sure
you go to the Chevy Dealer to get the new Pan Gasket, and Filter.
I once bought these parts from an Auto parts store, and although they
were labeled Delco parts, the kit came with a wimpy Cork Gasket, which
was junk, and was not what the Tranny originally used, which was a much
more heavy duty vulcanized/rubberized Fiber/paper gasket.

Definitely use the proper Torque Wrench, proper torque values, and
torque sequence on the pan to eliminate the chances of buckling the
gasket which will cause leaks. (Usually these pan bolts torque at about
18 ft lbs or so)

As far as Differential Fluids go, Mobil 1 full Synthetic gear Lube
should work fine in both front, and rear Differentials, even with the
limited Slip Axle, which you probably have in the rear.

An easy way to do the fluid swap on the Differentials without resorting
to ripping off the covers, is to buy a fluid suction gun,  use a length
of rubber hose insert into the fill ports, and remove the old fluids
this way.  Mark

Thanks all for the info  especially Mark D as I wanted to know about
synthetic differential and transmission fluids also.