What is killing the shoot tips on my peach tree
That is Oriental fruit moth. In southern Michigan, there are 3 to 4 generations a year. The first generation comes out at bloom time before there are any fruit and attacks the shoot tips and kills them burrowing into them. I have seen them attack the shoot tips of other trees such as apples. Generally the later generations attack the fruit but if there was no fruit around they will continue to attach actively growing shots.
Here is a fact sheet on this pest