@StretchNutz
First off, kudos for your parking lot grievance. There was something wrong, based on the details you gave, and you handled it when mangament wouldn't. Whatever contract language you used to settle it I'm glad it worked out for you.
This situation is much different, filing like
@542thruNthru said probably won't do much for you. Management has the right to run the operation as they see fit in accordance with the contract. As agravating as it is that this guy is somewhere easy, it's not a violation. Your best bet if you are looking to move is to get on a preferred jobs list. Now again, that doesn't mean you can bump someone with less seniority than you that has already filled the position. It makes you eligible for the next available one, at least that how it worked on my preload. As others have said, each building and supplemental language is different.
Lastly, don't work slower, work
safer. Not sure what numbers your pulling, but if you go from loading 250/hr to 150/hr I've seen guys brought in for sabotaging the operation when they get pissed and announce it. A gradual, more deliberate loading style will be better on your body and get your desired results without outright tanking causing other issues for you. All the safety methods they teach you, make sure you use them. A package needs tape, tape it up. Scan every package and load each one right away, no stacking at all. The list can go on, but you should get the point. Most everyone skips something, start doing it 100% by the book and you should get the results you want without screwing yourself.