you may have a point about bump steer. that was neither thought of, or checked.
i have a dual gauge toe plate i used to check that when i designed and built the front suspension for my 33 dodge humpback panel truck [the ENDLESS project ] i'll have to dig that out and check the toe curve as well as the camber curve.
i should also point out the reason we went to tube control arms was the original arms were modified for the bagged suspension.
however, both suspensions have the same characteristic symptom.
i thought about the guy running the machine as well. however, this shop has been around for at least 70yrs [and maybe longer], and it has a stellar reputation when working with all types of modified rides as well as heavy trucks.
still more ideas you bring to the table for us to try, and we THANK you !