Follow the vac line up from the trans actuator. It goes to the Switch-Over Valve.. most likely problem is the element is leaking at the actuator/servo.

As GVB suggest, get some vac to the the element for testing
I just pull the two lines off the SOV and put them together.. this eliminates the SOV and ECU and gets vac directly to the tranny.. take it for a ride and see if the shift delays.. if it does , you have confirmed the servocable as OK ..