2005 Silverado. Want to replace radio but need to unlock anti-theft feature

[alabamatx]

I have a radio from a 2006 Silverado that I want to install in my 2005 to replace the original that has a problem. The issue is that the 2006 is locked. I have seen lots of posts explaining how to unlock a GM radio but none seem to apply to the radio supplied in my vehicle or the 2006 model, although it seems to be a common model. The steps call for pressing the first an second preset button the get the first 3 digits of the  radio code and pressing the AM/FM button to get the other 3. Well, nothing happens when I press the preset buttons and furthermore this radio does not have a AM/FM button. The BAND button is used to select AM FM Sirius etc. So, does anyone know how to unlock this model except taking it to the dealer (which is too expensive for this). Thanks for any help