The Gospel of Truth has its value -- as a record of what early Gnostic Christians made of Jesus. You can read the Gospel of Truth and see what the early Gnostic Christians considered to be important. You can see how, in their own way, some schools of Greek philosophers longed for beauty, truth, perfection, and fullness -- even joy -- and found these in Christ. It's a testimony to how Christ fulfilled more hopes than those of the ancient Jews who wrote the New Testament.
What you will not find in the Gospel of Truth is anything like historical information on Jesus. No places are named, and no events are recorded -- though it does assume the reader is familiar with some of Jesus' life and teachings from other sources. The text is mainly a commentary on theology and philosophy, and how true knowledge of God through Christ changes our views of that. If you are looking for historical information on Jesus, you will not find it there.