1. We have all been through what you are going through.
2. What you are going through will never change. Screwing drivers out of their lunch and breaks is the basis of UPS's core business model.
3. Bullies seek out weak targets and avoid strong ones. If they turn up the heat, you need to turn it up even hotter. Learn to adopt the attitude that you can make them more miserable then they can make you. Become involved with your local union, and learn the facts about what you can and can not be fired for and how UPS typically handles disciplinary cases involving production issues. You will learn that, if you follow their methods and do the job safely and honestly, any threats they direct at you are hollow.
4. Dont buy in to what they say about "allowances" or "demonstrated performance"...these are imaginary concepts that they have fabricated in an attempt to intimidate the weak-willed into donating their lunches and breaks to the company. Remember that its all about your lunch. They want an hour of your labor for free and they have developed a very elaborate system for trying to bully you into giving it to them. Its a scam. Dont get ripped off, dont get bullied and dont allow yourself to be intimidated.