RE: Vin check to determine package and options?
From the 2005 CTS Service Manual;
Digit 1 country of origin 1 USA
Digit 2 ManufacturerG General Motors
Digit 3 Make 6 Cadillac
Digit 4 & 5 Carline/series DP not sure, my book shows DM, DN, DR. CTS, CTSI, CTS- RHD ?
Digit6 Body style 5 Sedan, 4 Door, 4 Window, Notchback.
Digit 7 Restraint System 7 Active manual belts w/driver and passengersupplemntalinflatable restraint front and side
Digit 8 Engine type 7 RPO LY7 3.6 L V-6 SFI
Digit 9 Check digit varies no other description
Digit 10 Model year 6 2006
Digit 11 Plant location 0 Lansing MI
Digit 12-17 Plant sequence number 181144
To find out what options a car has you need to find the RPO Code List. On a 2005, its on the Service Parts ID Label located on the bottom of the spare tire cover, in the trunk. It lists all the option codes that thecar comes with. I have a partial list in my service manual. Since you're looking at an 06 they may be different as your VIN seems to be slightly different than my book says. As an example, LY7 is the 3.6 engine. M82 is an automatic transmission. Actually I cant find an option code in the book for luxury package, or sport package. But my window sticker lists the 1SC Equipment Group that includes both the luxury and sport packages. The Sport Package includes Sport Tuned Suspension, Stabilitrac 2.0, P225/50R17 W rated tires on Polished alloy wheels. The Luxury Package includes Wood Trim, Memory Seat, Compass in mirror, 10 way pwr seats w/ lumbar, Heated Front Seats Universal garage door opener and Theft Deterent System.
I don't know if any of this helps you or not, but best of luck in your search. I love my 05 CTS!