Can you swap a 2004
GTO rear end into a 2005
GTO. The rear end in the 04 is fully built with every after market part you can get so it's not stock.

 

I "think" the rear ends from 04-06 are the same....but the axles are heavier in the 05-06....I "think"

 

all of the center sections should interchange. supposably the 05 06 has bigger axles than 04 but i believe they all have the same part #.

 

Yep, they are interchangeable. Ask me how I know, lol.

 

04 diffs have machined slots for the wheel speed sensors on the axle stubs and a smaller yoke bolt pattern to connect the driveshaft. Just swap the yoke from your stock diff onto the one going in. There is a write up about getting the correct "torque" on the retaining nut over on LS1GTO.com in the DRIVETRAIN section.