Yes, you could. It is a case of negligence or an intentional act but under the facts you describe you should be able to pursue a case against them. The employer clearly put their own interest above yours and, essentially, forced you to haul the cargo when they knew or should have known it was over the capacity of your truck.
You could sue them for the damages you incurred plus, if your lawyer can argue that it was a breach of contract (which is feasible) then you could recover your attorney's fees as well.
You can find a lawyer by going to www.lawyers.com and in the section for Area of Practice enter Civil Litigation or Consumer Law. Either of those will have the skill set you need.
You don't mention how much the damages were but up to $10k it can be filed in Justice of the Peace court but above that and it would have to be in either County Court at Law or District Court.
If your question has been answered then I'd offer my best wishes to you and ask that you please not forget to leave a Positive Rating so I receive credit for my work.
Of course, please feel free to ask any follow up questions in this thread. I want to be sure that all of your questions are answered. In addition, once you issue your Positive Rating the question will lock open and no longer time out so you can come back to it anytime in the future if you think of any follow ups.