The Tesla Large Drive Unit Gear Set 4.5:1 from Zero EV replaces that shaft (so the original shaft must be removed to install the new gear set), and that product web page has an installation video. The video shows the original shaft already removed, so it doesn't directly help, but it does show how the retainer works (but you have already removed that)... and the people at Zero EV might have some suggestions for pulling the shaft.
One potential idea: since the retainer plate fits between the gear and the housing, a custom plate for pulling could also fit there.
The problem with the gear puller is that is based on a screw pushing against the centre of the end of the shaft to pull something off of the shaft, but in this case you are removing the shaft (complete with the gear which is integral to it), so there is nowhere for that screw to push on. You need to use inertia (a slide hammer), or push against the motor housing.
One potential idea: since the retainer plate fits between the gear and the housing, a custom plate for pulling could also fit there.
The problem with the gear puller is that is based on a screw pushing against the centre of the end of the shaft to pull something off of the shaft, but in this case you are removing the shaft (complete with the gear which is integral to it), so there is nowhere for that screw to push on. You need to use inertia (a slide hammer), or push against the motor housing.
