Supposedly Delphi is owned by GM. Further, they are both in Saginaw, MI. Look at Delphi's website. However, when they installed my new box the shaft on the Delphi was slightly longer. I know because there was NO space for the Pitman arm removal tool on the GM box and there was approximately 1/4 inch space on the new box after the Pitman arm was tightened. So there is a difference in the physical dimensions of the box. I don't know about the internals. I'm confident some changes were made there also because of the difference in driveability.
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2001 HO 6 spd 2500, 4. 10 LSD, Towing Package, Electric Brakes, SPA EGT/Boost Gauges, Running Boards, Fog Lights, Real Backup Lights, Running Boards