6cyl;
There are 2 gears that control speedo rotation: the drive gear, which is internal to the tranny and requires a tear-down to change out: and the driven gear.
The driven gear is easy to remove, takes about 2 minutes. It's a little plastic thing and is colored coded as to the number of teeth it has. You can count the number of teeth yours has, add 20% and that's the gear you need. Example: yours has 10 teeth. 20% of 10 is 2 (better check my math on this). You'll need a 12 tooth gear. BUT, it's possible they don't make a gear as big as you need, in which case the drive gear would need to be changed (I think there are 3 different drive gears).
Costwise, changing a driven gear is the way to go, it's cheap and easy. If that's not possible, rather than tearing into your T5, I'd look at the adapter you mentioned.
