The 3.73's are fabulous for acceleration in an A4 but are a bit too much (3000 rpm @ 80 mph w stock tires) for the highway over 70 (2600 rpm). I was going to go back to my 3.42's until I heard about the Gearvendors. Now my A4 is an A5 with 3.73 going to 2.91 at the touch of a button. I have pics if anyone is interested. The install on the 4L60 is almost identical to a TH 400.