I think you may be on the wrong forum for that particular vehicle. Which brakes are locking up? Front or back? I have heard of the park brake pivot lever under the vehicle rusting and freezing up because its open to the road debris and seldom gets serviced to prevent that from happening. What ends up happening is you'll set the park brake but when you release the park brake that pivot lever underneath doesn't return which keeps the parking brake engaged. There has also been some issues with the brake caliper slide pins freezing up causing the brakes to prematurely wear out. With the mileage your vehicle has I doubt it's any of the issues I mentioned, especially if your brakes are randomly locking up while driving. There are a whole host of other issues with those vans but they wouldn't be the cause of your brake issue. The list of those issues are too long to list here. I'd suggest taking to the dealer and using the warranty to fix it. Now, no offense but in my opinion the promaster van is one of the worst vehicles on the road so I wish you luck
