I am surprised you are still getting "clings" but maybe in California, peaches are grown
year round and clings are grown.
Here in the Carolinas our peach season (only 1) progresses from clings to freestone with the latter beginning in late May or June and after that it is all freestone.
I have made jam for years doing this recipe, except using powdered Sure Jell and not liquid pectin. Follow the directions on the pectin package for the exact amount of boiling of the pectin.
This year I have done mine differently using MUCH less sugar with amazing results of a very peachy preserves and great flavor. I gave the recipe a few days ago again. Easy and very delicious. You don't get the number of jars because you only use 2C sugar instead of more.