Here's the problem with your approach to this. You had a powerful experience when you were five years old, an age at which children are not known for being especially rational thinkers. I'm not going to tell you how you should interpret an experience like that, but you really shouldn't set your mind in stone that it was caused by God or Jesus simply because that's the conclusion you first reached.
You said, "I can remember saying a prayer and experiencing an authentic feeling of joy like that which Christians often talk about." Well, fair enough. But can you be sure that you didn't have this feeling of joy simply because you expected to have it, based on what your mother had been reading to you? What we expect to happen because of something often causes us to interpret what actually happens in a way that confirms our prior expectations.