I have a 2013 GT stock and I seen my LTFT go to 15% also depending on the weather and condition, but never pass that. I also thought something was wrong too since I'm used to no more than -/+5 adjustments in the past for stock cars usually but I guess this is normal.
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2013 Deep Impact Blue Metallic MT-82 401a
DiabloSport in tune - AirAid CAI - SVT GT500 AB - Ford Racing P springs - Forgestar F14 - Roush rear/side splitters - Stillen chin splitter - CS Fascia conversion - LED fog delete - 2 much 2 list.... Official mod addict: D