6.2 is what we target for apples, but in the 6.0-6.5 range is acceptable. Too much nitrogen can be an issue as it focuses growth on greenery and not on flowers. You may also have a boron or calcium deficiency but a soil test will tell you that. The soils lab at U Vermont can test your soil and make nutrient recommendations (https://www.uvm.edu/extension/agricultural-and-environmental-testing-lab). You may also want to see if your local extension office has Master Gardeners who can come out and look at the tree to see if there is anything they can see in person that might indicate an issue. (271 North Main Street, Suite 110, Rutland, VT 05701-2424. Phone:<personal data hidden>