Is this something that has worked for you in the past? A minute of time online tells me there are people who would recommend this as a way of preventing side stitches but it doesn't seem to be anywhere near the first recommendation and I can't recall anyone ever solving this problem with more core work. It's not as though your core is in rotten shape, though perhaps there is still some possible benefit in running speed in strengthening it more, leaving aside any help it may be with cramps.
Good point. I will do what I can until I find something that works for me. Next time I get a stitch I will experiment with various breathing techniques and try to find something that works well.