I have found that PF labels for shared equipment for the allergens we deal with. However, I do not know about a GF environment.
I wonder if FAARP tests for gluten. You might look it up. If so, you woukd send them what remains of a package that you have eaten and had symptoms afterward. They analyze it for free and give you a report. I believe they contact the manufacturer and the FDA, too, but I'm not sure.