A904 Hard 1-2 Shift and Reverse

It's not the kickdown; kd affects both shifts. It's probably not the front band either, but adjusting it is simple maintenance. A shift kit isn't going to cause a late hard 1-2 shift and leave the 2-3 shift acceptable; unless it was installed wrong. If the front band is super loose; causing the late hard 1-2, then there should be spinup between 2-3.