Unless you want to get a PLC resistant tree, your current tree doesn't need to be removed. PLC isn't a systemic disease that affects the tree for life. The fungus floats around in the environment Immunox isn't rated for PLC and will have no effect on it. However Fungonil should have done the trick for you. It sounds like you may have gotten the Fungonil spray on too late. The tree needs to be fully dormant when you apply the Fungonil. I hate that you lost yet another crop, but next year spray the tree with Fungonil in the fall after it goes dormant, and then sometime in VERY early spring, before the buds swell. Fungonil needs to be on the trees before they wake up.

You need to spray in fall as soon as the leaves fall and preferably again in the spring at first bud swell. Any later does no good. Your spray this past year was too late. If you google peach leaf curl control you will get more info like below. Here is a link that might be useful: peach leaf curl disease and control

It can but seldom does, at least around here. But you need to begin dormant sprays every year when the plant is dormant. Any general garden center will have suitable products.

shp: Peach leaf curl will not kill your new peach trees. I would not replace them! Curl is caused by a fungus Taphrina deformans. The fungus overwinters on the entire tree (stems, trunk ect.). The key is to spray copper or a fungicide containing chlorothalonil in late winter-early spring before the buds even swell. Nothing you spray now will eradicate curl once you have it. The deformed leaves usually fall off in mid-summer. Wait until next year and spray while the tree is dormant. Not sure what the conditions are in New Jersey, but the peaches I grow here in WI are far easier to grow than apples! Pest wise that is. With peaches, I spray for curl, spray for plum curculio (late may-Mid June) and then I am basically done. So far no brown rot and only had some bacterial spot once. For me, I can grow peaches with a lot less spraying than I have to do for apples. I suppose the fungal/pest issues on peaches will vary by the region you are in.