It's a torque tube setup, right? The only way to get the pinion gear out is to remove the complete rear end assembly from the vehicle, loosen the three setscrews just behind the torque tube, and use a block of hardwood and a BFH to drive the driveshaft and the pinion gear out of the housing toward the back. The pinion gear and the driveshaft come out as an assembly. You might be able to do it with the axle housing in the vehicle, but it's definitely the hard way!
Jerry