I think you're taking the wrong approach. I think if I were in your shoes I'd ask for a raise. Don't complain about the fact that you have to do the heavy lifting, merely state that you're doing everything the others do PLUS the heavy lifting. Therefore you deserve a bit more than them. I think management and possibly even your coworkers wouldn't have a big problem with that. That is as long as it's true. The problem is not that you are being discriminated against, the problem is that you're not getting equal pay for equal work.
Good points Pappy, with the exception of thinking the other employees wouldn't be upset if Badger got a raise and they didn't. Badger what you describe happens all the time in one form or another, all employees with the same job are not equal, some are hard workers, some are not. You've expressed your point of view with management and they don't seem to care, so continuing to push the issue will only make you the bad guy. Go to work, do your job, and don't worry about the others.