Rough downshift under load

[moneylessrec]

I've been having problems with this thing for about 7 months now. Started as a very slight grinding sound sporadically when it shifts and a sporadic rough idle, no code. Changed transmission filter/fluid, helped for about a day, and was right back to same things, same when I cleaned the MAF and throttle body. It began to lose power, then finally threw a catalytic code (bank 1 P0420). Changed upstream o2 first, then cat (wasn't getting a reading from o2, so I changed it. Still don't get a reading from it). Fixed the code and loss of power. Finally the slight grinding just went away. Now it's developed a shudder when downshifting under load with low throttle input. Going up an incline with barely any throttle, it feels like it disengages, and doesn't mesh well as it tries to re-engage. Seems like a specific range of RPM. TPS? Need to swap transmission fluid again? I'm at a loss, and am kind of frustrated.

Also, this happened right before I moved (maybe 1-2 weeks before), and now my daily work commute is over a bunch of hills that are exactly what cause this problem to surface.

[moneylessrec]

No ideas? Still happening.