I purchased the item back in Feb 2008.
Yes it installs in the left side of the truck. Depending on your configuration, you may need a extra bracket .... its plug and play ... and then code for CD Changer
Yes, it definitely plays Mp3 CDs. Infact it plays them better than the front CD player ... as it supports bit rates all the way up to 320kb/s ... where the front CD player (in 2008 anyway) is only up to 256kb/s
As far as price ... list on this is $725. Circle do it for $550 ... so I'm giving you a fair bit of discount already. It didn't get that much use, as my car also had ipod, HD radio, satellite radio and of course regular radio and front CD !!!!