Which ever grade you decide, strongly consider becoming an Amsoil preferred customer ($20 a year) and you will recieve wholesale prices. For example 1 quart of Signature series 0W30 is listed at $10.10 per quart on the web site, but for me being a preferred customer I get it a $7.75 so the $20 Preferred Customer deal is well worth it. Buy one case and you more than break even.
Oil weight and brand is almost as touchy a subject as religion and politics so that's on you. Do a search on LS1 tech and you'll get more info than you can reasonably digest in one sitting.
In my Firebird I have run Mobil-1 10w30, Royal Purple 5w30, Royal Purple 10w30 all with no problems. Next I might try some Amsoil 0w30 myself, but we'll see.
In my Dodge with the big CTD I run Amsoil 15w40 and do extended drain intervals. I change the oil in that pig every 15,000 miles. I do have oil anaylsis' done along the way just to make sure everything is ok.
If you really want to know what's going on in your motor, get your oil analyzed at
Blackstone Labs
http://www.blackstone-labs.com/gas_engines.html
or
Oil Analyzers Inc. (I think they are owned or strongly affiliated with Amsoil)
http://www.oaitesting.com/
I have used Oil analyzers in the past for my Dodge Diesel with excellent results. If you use the same service you will build a history and be able to compare trends over time.
Another major site for oil analysis and lots of in-depth info is Bob the Oil Guy
http://www.bobistheoilguy.com/
That side is heavy duty, get your chemistry book out, your physics book out and clear about 6-8 hours in the schedule just to get your feet wet.
Chris
