new 42rh a500 rebuilt transmission problem

Just for curiosity, how much driving did it take for that to happen.
Yesterday,I was looking for a hydraulic reason for that 2nd to not be releasing, and just couldnt figure it. Today I know why. It wasnt a hydraulic issue!
Sorry about your trials. I know how you feel.
Its sometimes a little difficult to feel when all the clutches engage. I can usually count them as they engage and when its right, the front clutch assy rocks on the washer differently than when it rocks on a clutch. But the disengagement usually occurs during the install into the case. I stand the case up on its tail, to install the geartrain as Im sure you did too.
When I drop the clutch stack in as an assy with the band on, I make real sure to not snag the front clutch on anything, and keep thumb pressure on it as its going in, and steer the assy with my other hand to engage the sunshell slots.Once its down, I again check the rocking feel.Hope that helps
Im surprised the pump went in ok. Usually if a clutch is renegade the pump wont seat quite right.
I prefit the pump to the tranny with the bolts loose before the geartrain goes in.I use line-up pins. I smear o-ring lube all round the pump house and liberally coat the big o-ring.Just before I snug the bolts up from inside the case, I verify that the outside bolt holes all accept their bolts. Next I pop the pump assy out and torque it.Now it will practically drop home. I use the line-up pins again for final assy.
I guess it wouldnt hurt to check the sprague(over running clutch), since you say you previously had a couple of rollers fall out.
Ok so better luck second time.