Why did you add leaf springs? A 10,000 pound trailer probably has a 1,200 to 1,500 pound tongue weight. That should be well withing the payload capacity of a 2500. Are you using a WDH? Is it adjusted right? I agree, put some good shocks on it, Bilstein or KYB Mono Max.
How much air are you running in your tires? If you have them inflated to 80 psi it is likely too much. Weigh the axles and consult a tire load inflation chart and inflate accordingly. I would be 65 or 70 psi would be about right.