Under Grace, is your forgiveness by God conditional on forgiving your neighbor?

No. Under Grace, God's forgiveness is not conditional on first forgiving your neighbor. The Law demanded forgiveness of others before forgiveness from God, but the Apostle of Grace writes that God forgave us whether or not we forgave our neighbor (Ephesians 4:32).

Les explains that the petition about forgiving debts or trespasses was connected to Law. Under Law, a person could not be forgiven until he had forgiven the other person; that is what Law demanded, and that is what the religious gentleman described when he said, "I have to forgive them, because if I don't I can't be forgiven, that is by God." Then Les turns to Ephesians 4:32 and points out that this is the Apostle of Grace writing, the same apostle who said in Romans that believers are not under Law but under Grace. So Grace says that whether I forgave my neighbor or not, God forgave me.

Ephesians 4:32

And be ye kind one to another, tenderhearted, forgiving one another, even as God for Christ’s sake hath forgiven you.

Under grace, is God's forgiveness conditional on whether I forgive other people?

Under grace, God's forgiveness is not conditional on whether you forgive other people. The Law required forgiving others before being forgiven, but grace shows God forgave you whether you forgave your neighbor or not. Ephesians 4:32 presents this contrast, so forgiveness is not earned by first forgiving others.