I hope someone can help . I picked up a 1997 procharged 4.6 a few days ago an the Speedo is off . The place I got it from said it has 4 10 gears . now I have talked with a few different people at American muscle one said Speedo gear the other said Speedo recalibration tool . Which way should I go ? Also do I need a handheld tuner for the car if I go get it dyno tuned ? It is running rich