It sounds like you are going to try the 3.73 first. I think after you drive it for a while you will realize the Jimmie is happier at higher rpms than at lower rpms. I have always found a 13 speed and a slower rear to be ideal for a Detroit. You have the startability of a deep gear and it eliminates the 9th to 10th gear gap that really bogs a Detroit on an upshift.