Can't say I've ever really noticed stomach issues post race. I tend to either run before I eat lunch so I guess a good 4 hours after breakfast, or no more than 30 mins after I have a light breakfast.
I have however, several times, post race gone for a meal and decided "yeah a beer would be nice" and get hit with a massive headache I assume from dehydration (as that's usually the only time I get headaches). Last race I even drank several bottles of water post race to no avail. I might learn next time....but probably not!
FT, hope your new shoes help. I use to suffer from shin splints early on and it was due to heal striking, a few weeks of slowing down and working on form and it's never come back.