When I tune the LS engines, there are 2 sets of timing tables. One with much lower timing figures. The computer will revert back to the lower numbers when the knock sensors pick up anything. Generally the slight loss in power and MPG isn't even noticed by most owners.
I know the truck timing tables are extremely conservative due to the intended purpose the trucks are built for. I haven't been into the tunes on the newest trucks much past 2006, but I would assume not much has changed.
Some tuners will copy/paste the high octane timing tables over the low octane timing tables to keep everything consistent, and still leave the knock sensors active to pull 3-4 degres when knock is present. But at this point I wouldn't recommend running the cheapest fuel in it.
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