speedo adjustments

Any Ford Performance parts store should have a speedo gear. If not Powered by Ford in Orlando Fl, has them. 407-843-3673

The gears come in different colors, each color is a different number of teeth. To complicate matters, the gear on the transmisson output shaft can be either a 6, 7 or 8 tooth according to Hanlon Motorsorts, a major transmisson rebuilder for 5.0's. That causes some problems getting everything to read correctly. Toss in the variables of tire sizes different from stock and it can get crazy.

See http://www.hanlonmotorsports.com/t5speedo.asp for help on the speedo gear.

Check to see if there is a speedometer shop in your area. If there is, ask about the Stewart-Warner speedometer gearbox. I believe it is either a 777 Series Drive Joint Kits and Parts or 666 Series Drive Joint Kits and Parts. It is a small gear box that fits between the speedo pickup gear on the transmission and the speedometer. It has quick change gears that allow you to choose almost any tire size and rear end gear ratio you want. This will allow you to get the accuracy with within 1%-3%. The drawback is that it isn't cheap.
Please excuse the typo (their's, not mine) in the following picture - it should read Custom ratio adapters, not Custom radio adapters.

See http://www.gaugeguys.com/ratioadapt.htm for more info.