Ford Repair: gear change, dallas mustang, wheels and tires

Question
i have a 1999 gt 500 4.6 5spd i put i 4:10 gears
and no one can calibrate the spedo not even the
ford dealler? can you help? stock wheels and tires.

Answer
Chuck-

  Well...while I'm sure Ford didn't make a Mustang under the GT500 name in '99 (there will, however, be another one in '07), I imagine it's the same standard '99 equipment.  A retailer named Dallas Mustang sells a speedo recalibrator.  It can factor in gears, tires, wheels, etc.  I'm not sure exactly how much it sells for, but I think it's in the $100 neighborhood.  Hope this helps.

Steve