getting the gears installed monday...i've gone to a few trans. shops around here looking for a 23 tooth speedo gear....a mechanic told me that if i dont change the tail-shaft gear i'll ruin my car because that and the speedo gear wont be the same...is this true?...also he said it will be way farther off because my car is a t-5 rather than an aod....is this true?...also anyone know where to order this 23 tooth gear from?