Slow emptying stomach is also identified as gastroparesis. Sometimes the word Motility (ie slow motility) is used (instead of emptying). You can search on those topics and likely find some more info. There are a few motility drugs that help, reglan is of course one with some side effects. There is at least one other that is not approved for sale in the USA (domperidone). If you have any issues with reglan, I believe the other can be obtained, talk to your doc about it. One antibiotic has a motility side effect, that helps temporarily for some: erythromycin.
Outside of that, I've only read of some experimental treatments (like botox and/or stomach pacemaker) for serious cases. Keeping a diary of everything you eat and then avoiding foods that cause issues can go a long way in managing things. Depending on what the suspected cause is (viral, diabetes, surgery, unknown), the treatment may vary.