Copper it would be great if you could pin this!

If you want to know what rear end your Aero has, look on the driver's side door jam for the tag with the VIN on it. It will also list several other bits of info, including your Rear Axle Code which will be a two digit code. You can translate that code here:

Code Ratio
Conventional
22 4.10
23 3.45
24 3.73
25 3.27
26 3.55
Traction-Lok
B2 4.10
B4 3.73
B9 3.55

 

No power off the line, but a code 25 with a very good highway 3.27 I believe is where its at. My 3.73 is cutting it at 18 MPG with my 4.0