This is a "yes, but" answer. Yes, the will called for the slaves to be manumitted. However, Lee felt duty-bound to return home and work the plantation (and the slaves) in order to pay the estate's debts and fund Mr Custis's bequests to his granddaughters (Lee's children).

The slaves were not released until shortly before the war began. They were unhappy about Lee's management, and Lee mentioned to others that they were a "troublesome property".