you gotta keep at it with the dealer. They replaced a bunch of rear control arm bolts on mine and did a whole procedure to align the axles from the beginning like it was just built, and now I'm running a stock stabilizer, higher pressure in the tires, and it stays in its lane, tracking like a Ford e350 thats new, not 50000 in where where you feel like you're in a 2 hour tennis match with your left arm.
I suspect some of these came like mine, with a rear axle slightly out creating a thrust angle, and they fixed it at the factory by jiggering with the front alignment, which due to SAI and other angles will not work 100%. Insist on a complete alignment.