Chryler Mini Van downshift

Have a 88’ Chrysler Mini Van 3.0L. With about a 100K. Half of the time when I pullup to a stop sign the tranny will not downshift on its own and I have to do it manually. Also in the morning the engine will have to warm up before it wants to slip into reverse. Once warmed up though runs and shifts up through the gears without any noticeable slip. Filter was changed recently and most of the fluid replaced. Any suggestions besides a rebuild at this point?