What is the difference between gm part numbers for a 2003 cts radio one number is 25 750 438 and the other is 25 741 528 both radios are type gmx320 l1.5?

I can't tell you the difference but I can say from experience that you MUST replace your 2003 radio with the SAME part number that it came with (Mine ended in 528). I tried using one that said it worked in a 2003-2005 CTS and it wouldn't work. The radio would play but only the volume control and manual tuning could be used. Nothing else would work. Sometimes it would start in AM mode and sometimes in FM. I called my seller (Discount OEM RadiOS in GA) and learned the hard truth. I'm in the process of returning it but am going to have to wait until they get the correct unit in. Good luck.