since I have bought my 2003 4x4 hemi I have used nothing but Chevron 90 in alaska that is all I could get was 90 now that i am in texas now I can put 93 and I use it know either chevron or shell that is all I will put in my truck and I get 14mpg realworld I do it every time I fill up.
The owners manual calls for the mid-grade 89 octane. Sometimes I will top off with the 87 when I am on a half tank. Never had a problem ! Anything more than the 89 is just a waste of money. You wouldn't notice any difference.
I found that if I use the Sunoco Ultra 94 or 93 ( cant remember which grade it is) it only costs about $5 more a tank to fill from empty, and I average about .8 miles more per gallon, and my tap went away as well
You need to use at least 89 because of the compression and timing advance. You have to use 91 with superchips because it advances the timing. I was using the 87 octane tune with superchips and i had to take it to the dealer, so I set my truck back to stock. It ran like crap on the 87 octane and stock tune.
No reason to use 91 or 93 on a stock truck though.