Your tree is not soursop but I believe it is cherimoya which like soursop belong to the same family of annona. Anyhow, to me it looks like it there might be a deficiency in nutrients if there is no presence of disease. When was the last time you fertilize it? It may need Magnesium as well. Your tree looks good right now but could look great if you address it's problem.

It could also be Atemoya.....anyway I think it's a fertilation troublem...may be lack of iron

And if you have mulch around the bottom of the bottom of the tree you might want to move it away from the main trunk as it encourages mold and ants which bring aphids and disease. I don't use any mulch around my trees.

In case you are looking for a soursop, you can tell it by its strong and unmistakable scent as well as the shape of its leaves. It grows easily and quickly from seeds.

Your tree is not soursop but I believe it is sugar apple