J.Y.
I had a really fast, strong letdown also. I would express some milk (by hand) before each feeding-just enough to get past the strong spray. I didn't want to increase my milk supply. Then, I would lay on my back with the baby on his tummy to nurse. I don't know if it was the gravity slowing the milk or the baby's position, but it helped prevent him from choking and gagging. My daughter adjusted to the letdown at around 4 months old and my son did at around 5 months old so that I didn't need to do those things anymore. At that point breastfeeding became much more enjoyable for both the babies and myself. Both of my children nursed for 2 years. I hope you find something that works for you and your baby.