Is there any way that the differential/driveshaft could be causing the issue? All of my bushings were totally shot, so I replaced everything, but now that all the bushings are tight and new, maybe slop in the transmission mount, or something could be causing it?

I've noticed that the directional change happens when there's a hard upshift, and it gets worse as I go higher speed.

I took care to align my differential bushings like the old ones, and the differential is sitting in front mount nicely...