IT sounds like you are trying to OVER LOAD it too much. A stock 250 /2500 in any class ..if it did not come with th eHD system then you may look at other reasons for your problems. Your WD units also may be too light for the job, Find the heavest weight bars youcan It may help,,,but also make sur your hitch is of a heavey enough size.
Best get to an expert to see what you need. That also may lead to structural damage down the road.
I have seen people try AIR bags, and over load springs and still get in trouble.
I have had Pick ups for over 40 years towing and TC, and if it ain't srong enough then change it out.
Well thats my 2 p.
Chuck