When I bought this truck (Ford 6.2L) I really didn't expect that it would need premium under any circumstances, and it may not really, but the manual recommends premium for towing and/or hot weather (funny they don't say what "hot weather" is) so since it is still new (warranty) and it is hot and I will be towing
I got my interest peaked and just went thru the 2012 owners guide checking on the above subject. Maybe went too fast but did not find that info. It does indicate that you should not get below 87 though and not to flip flop back and forth between E85 and E10.