I think tnthub pretty much ended the thread with his responce . In addition to all the stuff he said, you may want to try race gas. The reason I say this is because there is quite a bit of variability in pump fuels. Shell 93 by your house may be different from Shell 93 in another county on the same day. I know your car is mostly stock, but I would find a local (VP/Torko or equivalent) fuel distributor and grab a 5 gal pale and give it a try. Race gas is expensive (5-10 $/gal), but trying it out at the track might be worth it. If your knock is gone or the same everytime, you could atleast rule one more thing out
Good luck.

 

I don't know about using race gas in a stock LT1. If you are having knock problems, they need to be addressed and besides higher octane gas probably won't help anyway. The rule is use the least amount of octane you can without detonation, and this is on a properly running engine. I have 11.0 compression and use 92 octane pump gas with no knock and my car is very consistent.

Randy