Gastroparesis can be experienced by diabetics after many years because of the effect on their nervous systems. It must reach quite an extreme state to have such an effect IMO. My stomach shows some nervous system degradation but I believe that I have improved it recently. Check out the needed B vitamins which help nervous system function and maintenance such as B12. Chances are you might not be digesting B12 and could have a deficiency when your body needs far more than is available.
Try examining your iris around the pupil for a grey mark. Look closely and notice a difference in the colour next to the pupil and just outside it is the stomach zone, a grey marking here indicates deterioration of the nervous system serving the stomach. Lots of coconut oil and very recently beginning the GAPS introduction diet has helped to restore the area around the pupil towards it's normal blue colour. Still some grey but not as much as it was. There are more iris fibres which makes it less grey.
I believe that I have an helicobacter pylori infection which has had a big impact on my health. I want a test done for that first before I attempt to destroy it.
Fat is also very important, all those low fat diets and polyunsaturated fats are damaging people's nervous systems! Saturated fat is the best fat to eat. Coconut oil and animal fats are recommended for stomach problems and the nervous system.
Check out the GAPS diet as it might be helpful because it aims to rectify digestive disturbances.
I have experienced a smell myself on brief occasions but it came and went. I was also constipated for most of my life. Iodine has helped a lot in that respect. Iodine has anti bacterial effects so could help to naturally control bacteria in your stomach AND move your gut as well. Two problems solved!
You might have SIBO. I think it could be a permeability problem of the lower gut leaking into your bloodstream and from there into your lymph and sweating the smell of faeces. But worrying about the smell could prevent or delay resolution.