Don't put any of that crap from a bottle into your gas tank, it doesn't increase octane or clean fuel injectors for crap. Its a borderline scam really, i should have thought of it first LOL. The only way to add octane is to do what mike said, and as for fuel injector cleaner the best you could hope to do is a full injector flush or put an entire can of seafoam in the gas tank with less than 1/2 a tank in there, but even that doesn't clean them very well.
Keep using the 91+ octane fuel though, the 3.0L engine has close to 11:1 compression so i wouldn't put 87 in there IMO. The ECM could probably compensate for it, i just wouldn't do it.

 

I wouldn't drop down to 87 either, maybe 89 but at that point 10 cents more per gallon isn't going to break anyone.

 

See.. around here its the price for 87, 10c more for 89, but only 5c more for 91. So I stick to 91.

And, its all non-ethanol, non- reformulated, non- MTFB crap. Pure gasoline.

 

I only fill up at Shell as it is, I'm picky when it comes to gas. We have 87, 89 and 93 there. 93 is usually 10-20 cents more expensive than 87.

 

You are lucky, its 10c more for 89 over 87 and 12c more for 91. Just sucks that all of our fuels are worse then all other fuels sold at the pump in this country.

 

Since I'm in Cali I use only put Chevron or 76 stations 91 octane, is quite expensive I must say.