2010 Ram 1500 Rear End Sway/Oscillation

I recently purchased a 2010 Ram 4x4 1500 with a lift installed (I think its 4" or 6"). I drove the truck for several miles and didn't notice anything odd about handling. Then i got a load of mulch and driving home at moderate speeds (~40 mph) i noticed a pretty severe rear end sway/oscillation during turning. Basically it was fine when driving straight, but when I entered a turn the rear of the truck started to oscillate. The tires weren't sliding on the road, but the body was oscillating side to side. A couple days later I was towing a medium duty trailer (probably 1500 lbs) and noticed a lot of trailer sway. The condition is pretty severe with a loaded bed or a trailer so I'm looking for some advice on what it could be. it feels like the truck suspension compresses on one side and then it rebounds and shifts the other side and then keeps going back and forth. I usually have to slow down pretty significantly to get it to stop. I've seen some other posts on Sway Braces and worn shocks but I thought I would solicit some thoughts on my specific scenario. Thanks for any help.

Try some airlift 1000 bags in the rear coils. .