The statement that God is truth is deeply mysterious. Now the statement that God is love is also mysterious, but it is easier to get a start at what is being said:
- God isn't identical with our loving, but rather God is identical with his own loving, and our loving is but a participation in God's loving.
- God isn't identical with our truthing, but rather God is identical with his own truthing, and our truthing is but a participating in God's truthing.
I see two options: one reactive and one active. The reactive action is one that finds reality and unveils it (Heidegger suggests unveiling as at the heart of the etymology of the Greek aletheia--I have no idea if he's right as a matter of philology). The active one makes truths them true. If we're looking for something in God, the active one is more promising.
Here is a suggestion. God makes all truths true, though not always in the sense of "truthmaking". Propositions are divine ideas. Their ground is identical with God by divine simplicity. True propositions divide into the necessary and the contingent. Necessary propositions are made true by God himself: God is their ultimate truthmaker, and he makes them true by his being. So in the case of necessary truths, truthing is God's activity of making necessary propositions be true in virtue of himself. In the case of contingent truths, truthing is God's activity of making contingent propositions be true by creating the reality that grounds them.
Our truthing, on the other hand, is both active and reactive. Some truths we make true in the active way by being or creating the reality that grounds them. Others we merely react to. In both cases, our truthing is derivative from God's: our creative abilities are mere participations in God's, and require God's constant cooperation, and our reactions are ultimately reactions to God.
I do not have a great amount of confidence in this speculative analysis.