Slow engagement could also be caused by a sticky solenoid, or one that's in the process of shorting out the magnetic coil. The way it's supposed to work is that the solenoid pre-loads a spring, and as soon as the driveline unloads by letting off the throttle, the locking plunger snaps into place. It sounds like the magnetism is weak, or the plunger is sticky. You might need to remove the solenoid and bench test it.
Jerry
