I had ordered my strange 12 bolt back in April. I had it with the 3.73 gears. They called me this morning and said they had problems with the 3.73 gears making to much noise and needed more R&D on the problem. So they offered me a Dana 60 and shorter driveshaft for my troubles. I didn't think I needed a rear end that is backed by 6 second cars. So instead they told me they could put the 3.9 or 3.42 gears in it. I told them to throw the 3.9's in. Is there much of a difference in performance between the 3.73's and 3.9's.