I found a big long thread about this topic on Powerstrokenation and decided to give it a shot. lots of the know it alls there said 1oz/gal was what to use. I did this for about 3k till now since I am running about 50% bio. It helped quiet my truck down a little. the Bio makes my truck even quieter!
I was using the super tech stuff from walmart too. it was maybe 9 bucks for a gal of it.