I also notice while backing in reverse it seems to take an unusual high rpm maybe 2000-2500 rpm before its grabs likes that when it stalls and grabs. But in drive it grabs around 1200-1500. Its trial and error, these are the things you deal with when buying a unknown motor and trans from the junkyard and just take a chance on it performing.
Reverse needing more RPM's may be an indication of something wrong; those high reverse RPM's are quite abnormal. Reverse typically needs higher fluid use and will drop the internal pressures if something is wrong with fluid delivery or leaking.
BTW, what do you have for a kickdown linkage? Is it in place, connected, and properly adjusted?
