As said before but use only AC Delco plugs. Some say that Denso makes them, regardless the AC were the easiest to find. Use only AT2 fluid in the TC. Some talk about an alternative but I paid 7$ a liter at the dealer. If there was an alternative it would have to beat that price.
Engine oil: My oil life monitor gongs after 16000km or 10000 miles. It has no idea what I run so run whats cheapest that will work for your climate. I personally run synthetic and am going to stretch my oil changes out to 20,000km. I run it easy and do a lot of highway miles. I also use one oil year round to work in our moderate summer heat and extreme bloody cold winter. if cold flow properties do not matter just run some cheap conventional. I use Pennzoil Platinum 5w30 with a Fram Ultra filter.
As for the diffs: They spec synthetic from the manual. 75w90 GL5 front and back. No additives required if you have the G80 locker but would require some limited slip additive if you have a limited slip as in the SS model. I do not see how synthetic is required but I personally use it. it has better cold and hot properties and according to Eaton, gears run cooler and seals last longer. I run Amsoil 75w90 as it meets the GL5, was relatively inexpensive (15$ a quart) and has a really low pour point.
I have a Hastings transmission filter and the tranny had a fluid exchange with Amsoil low viscosity ATF. Why: It again has great cold flow properties and I got it for free.
Regardless, run whats cheap. You don't need the best high dollar fluids to keep this thing alive and happy.
