Recreational Vehicle Lpg Tank Valve/gauge problems of the 2009 Volkswagen Routan

Since purchasing the vehicle as a new car in October of 2009 we have experienced intermittent but chronically reoccurring issues with violent shaking during braking on our 2009 vw Routan. To work the problem the rear brake rotors and pads were replaced by the oem three months after purchasing the vehicle. The problem persisted & after repeated visits to the dealer the front brakes and rotors were replaced by the oem at 15,019 miles on October 27, 2010. Vibration during breaking still persisted at highway speeds but was manageable. In July of 2013 heavy vibration returned. The dealer informed us all four tires had uneven wear and would need to be replaced, along with all 4 air pressure gauges. Shaking continued so we then paid to have the front rotors and brake pads replaced again at 47,300 miles (appx) on August 6, 2013. As of now the vehicle still vibrates at highway speed braking although less violently. We believe several issues are at play possibly: - inferior or defective brake rotors, both factory installed and oem replacement rotors - chronic stability issue at highway speeds - uneven wear on tires which contributed to more rapid wear and tear - near simultaneous failure of all 4 air pressure gauges before 50,000 miles. We have kept the replaced tire pressure gauges, break rotors and pads if NHTSA would like to examine.