Q: What is the problem with my peaches? Is it brown rot?
A: Why do you need me to diagnose your problem when you do such a good job figuring out the problem yourself?
It is most definitely brown rot.
The disease is typically caused by sucking insects like stinkbugs or curculio weevils visiting a diseased fruit and then sticking their snout into a ripe one.
The disease is disheartening because it typically appears just before the fruit is ready to pick. It affects both peaches and plums.
The best cure is to implement a good insect control spray program now and each spring following.
Remember to spray insecticides only AFTER blooms are gone, in order to protect bees.
I don’t think you can control much of the disease once it appears but I recommend you spray the tree with myclobutanil (Immunox) now (in June) to get a head start on any disease control you can accomplish.