Ipod skips at high treble?

I have a new ipod 120gb clic that's hooked up with a usa spec interface for my car which is a 2001 grandprix, and I wanted to replace the factory radio with the same radio out of a 2001 firebird. (simple plug and play) The radios are the same but the radio out of the firebird has the aux on needed to control the ipod. It's the Delco Monsoon with the 7 band equalizer. When I play my ipod (ipod equalizer setting and volume adjustment is off) it starts cutting out if the treble is too high. I have to lower the treble which then causes the music to sound like it's coming out of a tin can. The treble equalizer on the radio itself is turned down to almost nothing. I searched and couldn't find anything on the web with my problem so hopefully someone can help. Does the radio not have the power to output? It should. Everything was installed correctly and I play my music just loud enough to hear while driving on the expressway so I'm no means blasting my music. Anything is appreciated. Thanks for taking the time.