are the 3rd gen 5.7L OE midpipes (cats and y) the same ?
ie: from 07-08 etc...

 

part numbers are different, 55366881AC / 55398203AA does that imply a change?

 

IDK if they are different. Best thing I could tell you to do is go to someplace with a busy parking lot and look under some trucks

 

I have been told that the 06/07 are the same and the 08 is different. This is according to Magnaflow. The midpipe is different because the 08 does not have a front resonator.

08 Y-pipe

 

looks like my 07 ?!
looks like ill have to test.

 

but the cat section the same ?

 

That's is so sad looking.

 

i haven't looked side by side. Magnaflow told me that the converter Y pipe section was made by a different supplier and was different. This is why their 16700 cat-back system for the 06/07 doesn't fit the 08. Well, I have this kit on my 08 truck and it fit fine.
I am pretty sure that the 06-08 are the same.
What are you trying to accomplish?