When running at max trailer axle weight or more, the tires are the biggest concern. Stepping up a size or even a diameter (new rims of course) would help immensely (provided you have the wheel well room for the larger tires). You will find that the tires are probably the exact same weight capacity as the axle. If nothing else, get a set of the best tires you can find for a trailer. I'm going to suggest Carlisle Radial Trail HD on the success of a co-worker with that tire, and I haven't read of problems with it. I think Goodyear also has a decent trailer tire.
Charles