Shy Girl, I am so sorry to hear of your problems.
I used to suffer from gastroparesis/delayed stomach emptying, all the typcial symptoms (google gastroparesis). But once I got my bg levels under control and managed to keep them nice and steady, the gastroparesis disappeared, thank heavens. Its a distressing condition, it makes you feel very ill and unattractive, I avoided people because I thought of myself as the most disgusting person ever.
Having food sitting around in the stomach, it begins to ferment, this can also be the cause of diarrhoea.
Delayed gastric emptying in itself doesnt cause high blood pressure, but the straining and vomiting and upset can raise your blood pressure.
Good advice investing in a blood pressure monitor, they arent expensive to buy.
You have had problems for such a long time now, I really do hope and pray that things get better for you, please dont hesitate to get in touch with me if you think that there is anything that I can do to help you, you have my email address already.
Big hug x