How long since you changed the filter?
How does the fluid look?
Bright red, or dark?
Dropping the pan (while changing filter) will usually lets you know if there is a problem.
Soft shifts don't necessarily mean trans is going bad.. unless something is "slipping".
Fresh fluid and filter is always first line of defense (and diagnosis).. and usually helps.
Sluggish shifts (in older transmissions) can also be remedied by a "Corvette Servo", which raises pressure to shifts. I have this in both my van transmissions for firmer shifts. This servo upgrade is replicable thru side of trans, without any further disassembly.
"Trans-Tune" by Seafoam is a great additive (before filter change).. I've also had GREAT success with this product.