I tried upgrading the final gear to improve the torque at low rpm but failed. Details can be found here. I got another used gear box from a scrapped 2004 156 selespeed model. The new final gear ratio now is 3.73 vs 3.56 in the original box. According to Automobile Catalog, the 2 boxes are the same except the final gear. Provided that the 2003 model comes with higher power and more torque with its direct injection engine, Alfa Romeo still put a higher ratio final gear. To me, it seams that it is a reification to a weak spot of the series I 156.
Spec. of alfa romeo 156 by Automobile Catalog
