We need more info to tell if you are overweight. Most likely you have an older truck if a dually diesel has a tow rating of only 10k. We also need the year, axle ratio, 2x4vs4x4, and ideally the trim package to get a good idea what your real tow rating is.
Also, is that the TT tow limit or the 5th wheel tow limit. They typically have different ratings.
Properly spec'd, 3/4 ton trucks can get up into the 14-15k range while staying in the ratings, though above around 12k, I would really prefer a 1ton SRW and by 15k I would want a dually.
Also, some people ignore the ratings.