Since you're using the distance correction, speed doesn't matter. It's more important that you use a long enough test distance (10+ miles) to help negate any small GPS distance travelled errors.
I have never had the need (or desire) to use the 91+ tune, but you should feel a slight hp/TQ improvement (IIRC it's 7-15 hp).
Was your gas tank empty when you filled with 92 octane? If it was, I would wait (to change to the 91+ tune) until you've used about 1/4 tank to make sure you have all of the 87 octane out of the system.
If it wasn't empty (or real close), I would wait until the next tank before I changed tunes.
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"Good judgement comes from experience. Experience comes from bad judgement." - Colin Powell to new batch of 2LTs (while serving as V Corps Commander)
Factory manuals here: http://www.motorcraftservice.com
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Tue, October 11th, 2011, 12:16 PM
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