Don't listen to some of these drivers who have years of experience, telling you they don't sort through their loads. Maybe they don't, maybe they do. Who cares what they do?
Until you gain seniority, don't take your lunch, skip your breaks and try to get a feel for how your truck is loaded. The preload is this company's Achilles heal. Nothing would make UPS more profitable by fixing the preload, but, unfortunately, they are just not interested.
So, that is what you have to deal with. Your preloader will either make you, or break you. So, you can try and talk to your loader, but that probably won't help much because chances are, he is loading more trucks than he can load with much quality, so he won't have much time to chat. You might try and go through your truck before you start. It might help, but it isn't without risks. One, seniority drivers might get pissed because working off the clock is a violation of the contract. Two, if you somehow get hurt working off the clock, you are on your own. No Workman's Comp. for you. And third, it sets a bad example. If you make seniority, NEVER work off the clock. If you get into this habit, you will find it hard to break. Your boss will start hammering you about performance, and next thing you know, you're finding and exploiting every shortcut in the book.
Having said all of this, your main priority is to gain seniority. Do what you have to to make it. Once you make it, however, ignore all of your shortcuts. Forget that you ever did them. That means, stay out of the back of your truck before your start time, NEVER skip your lunch or break and follow the methods you are taught. Management could care less about the methods, until you make a mistake. Then, they will beat you over the head with them. Bean counting is their game. So, make the methods your backbone. Not only will they keep you safe, you will find they will also make you more money.
Good luck, and be safe. Let us know how it works out.