Hi J,
I got super severe dw after installing a lift, new steering dampner, wheels & tyres etc and I know you don't want to hear this, but it really is a process of elimination.
Re threatening the Dealership, that will put them off side instantly and, if you've done mods, they'll wipe their hands of any problems you're having instantly, which they're legally entitled to do. Far better off to save yourself the grief & listen to the fellas around here