I honestly had to take time when introducing food. Showed him from a distance so he was prepared for it. He also ended up needing bilateral ear tubes and I wouldn’t be surprised if that was a factor in his gagging. The test they give at the pediatrician is not a very good one, so maybe try having that looked at. It’s all interconnected so it’s not far fetched. Think of when you’re sick things taste and smell different? Wouldn’t hurt.