The reason they said you should only run 87 is because that is what the truck is tuned *from the factory* to run. Anything over 87 isn't going to do much because nothing will be advancing to take advantage of the more stable fuel. Topping off with 93 ever so often is to help boost poor grade fills.
Your custom 91 tune is written to take advantage of the improved fuel grade with features like (but not limited to) timing and cam adjustments.
I dont know how reliable the techs are over there but around here a single oil change can cause your engine blow faster than a blower and a lead foot. Over here they like to make you a return customer.
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Wed, March 2nd, 2011, 09:23 AM
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