I guess I did not see the 89 octane note, - or just got too excited, and just installed it with 87 in it.
But if they recommended 89 over the standard 87, then I am sure that recommendation is warranted to avoid detonation.
I stepped up from 87 to 89 & that does the trick. As I said, a "more premium" fuel, or slightly higher octane. Does not seem to be much of an issue in the warmer months, but as it gets colder (I'm in MIchigan), I belive they may put some additives in the fuel and that surely does not help (seems to be worse in colder weather). If things are right on the edge (or you get questionable fuel, even from a reputable station), if you load your truck or pull a heavy trailer, you may notice some detonation. Also, engine loading at lower RPMs can also cause detonation (piston hangs around the top of the stroke a bit more where the charge has more time to heat up and then you get more multiple fires going on in the combustion area then you know what to do with at multiple times, creating waves banging into one another, which causes the knock). Different throttle responses in different parts of the RPM range are an input to that. So changng the response could very well be a contributor.
Ok - I'm over thnking this.
Just keep an eye out for detonation (or run the 89 as recommended).
Have a great day guys - It's Friday now.