Spur gear problem with strobe slipper

The pinion didnt have anything stuck in it, and the tranny was tight. I think Im going to get some right angle aluminum, something thicker than this motor mount, and cut myself a new one. Something that hopefully wont flex at all. But if the flex is in the chassis, that still wont help. I might make a sheet aluminum brace between the rear bulkhead and the tranny, or maybe a whole aluminum upper deck.