Gastroparesis or slow stomach can be miserable, particularly when one is trying to manage medication on a tight schedule. Diabetics can really have it rough, but it is bad enough with PD. I'm not sure if it is the disease or the meds.

In any case, I have had very good results with ginger extract first thing in the morning. There is decent Chinese research backing it up. Another that I haven't tried is rhubarb extract and, again, with Chinese work published. Yet another that I have tested and found promising is aloe although I haven't checked the literature. Finally, anything that tastes bitter (often the reason that it is in a capsule anyway) has the potential to be of help. The GI system responds when the bitter tastebuds are triggered.
-Rick