I am looking into purchasing a 2003 Mustang GT(Beautiful car and really like it!) but there is one slight issue, the tranny was swapped for a manual(was an auto at the start of its life) so the speedo was thrown off by this and apparently reads almost double. How hard would it be to change this? I do not have any software but the car does come with an sct tuner, the owner does not have the software either. Can I change it at all?