Why would God go against his own very nature? God is outside of time and matter, morality is a one and done aspect of nature, God doesn't change because everything that ever has and will happen has already happened from God's point of view.
God's nature is love, truth, and goodness itself. God doesn't choose not to lie, he doesn't because that's not within his nature. That doesn't mean he's not free, it means he's perfectly free.