I have an 07 Tahoe. I have been wanting to get a little better fuel economy out if it. When I started logging it last night I noticed a lot of knock. Most was about 7. I haven't done anything tuning wise to it yet due to this issue. I know the last time I had it serviced I heard the service writer telling a guy that has a new Tahoe with the 6.2 that he should be running 91. I was not told this when I bought mine and it doesn't say anything in the owners manual. Just wanting to get some opinions. I only have the 5.3 in mine btw.