2003 suburban 1500LS transmission compatibility with a 2009 1500 Silverado??

 

2009 is the start for the internal mode switch and deletion of the 3-2 downshift solenoid. So it would not be compatible. I've tried to put a 2008 into a 2009 a few years back and it was a no go because of the differences.
2000-2008 will interchange. You can put an ISS unit in a non ISS vehicle but you can't put an non ISS transmission into an ISS vehicle without additional tuning...

 

Thank you so much!