When reducing the gear ratio, you also need to reduce the number of teeth on the speedo driven gear. Assuming that your speedometer registered correctly with the 3.73, you need an 18-tooth speedo gear (3.27/3.73 * 21t=18.4). I dont' know if anyone makes an 18-tooth gear, but I know that my C4 has a 16-tooth, so there should be available gears in hte middle. Some transmission supply shops carry the gears. Take the gear in to the shop though, and take calipers with you to compare the dimensions of the parts.