Diabetes is linked with GP, and GP can cause abdominal pain. There are other causes of GP, some known, and many unknown/idiopathic. The symptoms seem to vary case by case, and by cause so it's hard to diagnose without that Emptying Study mentioned earlier. There are some pretty good GP support groups out there, and also a fair amount of information here if you search.
There are a few different options for GP treatment. Generally the first step is finding out what foods give the most problems. Keep a daily journal of foods and try eliminating various food groups for a week or more, and seeing if symptoms change. In general, I've read high fat and high fiber foods should be avoided. There are other items but really it boils down to experimentation. If in doubt, anything you don't need to survive (candy/sugary things, caffeine, transfats, saturated fats) should be avoided. If medicine is required, one thing you may want to look into is Domperidone. It's not easily obtained in the USA but it appears that doctors can still write a prescription and then you can get it from other countries via mail. IMO, it looks like a safer option than Reglan, the controversial aspects don't seem to be a factor for GP sufferers, but it's not sold here for the other uses.
Some natural items that you may want to search / investigate:
DGL Licorice - for nausea (chew-able tablets) <- works for me
Beets - Something about the Betaine and their ability to thin bile <- works for me
Artichokes - not sure on this one, but seems to be good in general.
Probiotics & Yogurt
Mineral supplementation (Magnesium, Potassium, Calcium, Sodium) - play a factor in symptom management.
I don't have first hand experience but have read good things about:
Ginger - for nausea (natural / real, not pills)
Zanthoxylum which is used in Asia as a motility treatment <- anybody have any experience???
Peppermint Oil - read up on it, it has many good effects but can make other things worse (Reflux).