I only found a brief mention detailing your stomach issues (gassy & gnawing) and this isn't typically the main complaints with autonomic GI problems. Maybe you mention other symptoms elsewhere, that I haven't read. But autonomic GI symptoms usually include early satiety (fullness), nausea, vomiting, pain/discomfort, delayed emptying, bloating, constipation, etc...all signs of dysmotility (which is the most common autonomic GI dysfunction).

Testing for this includes a gastric empty study, where you eat some scrambled mixed with contrast (you can't taste it), then lay on a table for a few hours while the nuclear imagining documents the movement of food. Results are based upon the percentage of food emptying the stomach within a set time frame (some tests are for 2 hours, some 3 hours).

Testing for autonomic dysfunction of sweating is the QSART (Quantitative Sudomotor Axon Reflex Testing) or Thermoregulatory Sweat Test (TST). Both are relatively easy, but they are typically only available at large academic facilities.

Hope this is helpful.