A833 Can't Downshift / Poor Performance

Hey Guys,

I am having a lot of trouble with a rebuilt ("rebuilt") transmission I bought. The trans shifts into gear just fine when idling in the driveway, and is marginal on upshifts (minor clash), but I can't for the life of me get this thing to downshift into gear while the car is moving.

I read through a lot of posts on here, and so far I've:
- Pulled the trans, inspected the clutch, cleaned/greased the input shaft,
- Tried 3 different fluids; ATF, 75-90, and 85-140 (no real difference)
- Checked the clutch disengagement (I can spin driveshaft by hand with clutch in, car in gear)
- Ordered new shift rods and arms, installed, and adjusted the shifter perfectly.
- Adjusted the stops on the shifter
- Checked the pilot bushing for binding (it is perfect and new)
- Checked the throwout bearing
- Pulled the side cover - shift fork for 1-2 had some minor wear on it, and reverse gear was a bit chewed (not from me), but nothing absurd. Actuated the shift collars by hand and it all seems to jive just fine.

Is there anything I am missing that I can try here?

*** Not that it matters, but I did try to order a rebuilt one from Brewers, but unfortunately they were backed up until September (when I called in March) and I wanted to drive the car this summer.
put the back on jackstands and go through the driving motions with the wheels in the air and see what it does..