This is a genuine AAM rear axle shaft for the 11.5 rear differential found in 1999-2002 GM 3500 2wd and 4wd pickup trucks. This will not fit a cab and chassis truck. Here is the application from AAM’s website:
40003202 AXLE SHAFT DW (1019MM; 30 TOOTH; 8 BOLT) LH/RH 2 C,K 1999- 2002