You probably need more / larger chocks. Though X type chicks are not designed to hold a trailer in place, they do help the other chocks hold the rig in place. Sometimes it is best to put down four chocks on the downhill side. Even put chocks tight against the wheels resting on the leveling blocks.
Another thing I do is after we have the rig level side to side but before putting the tongue on blocks - I start the truck engine, put the truck in neutral, release the parking brake and let out on the main brake. The truck and trailer tend to move a couple inches and go tight up against the chocks on one side.
After the movement is completely stopped I will set the parking brake, put the truck in Park and shut down the engine.
Only then will I put weight on the tongue and raise the tongue off the ball. I never unhook the chains until after I am sure the trailer is not going to move.
I also make sure the wife or anyone else is not behind the trailer or next to the tongue to get run over or hit by debris if the chains break.
When I was 15 my dad had me drive the truck and boat trailer from the launch ramp back to the campsite. In a hurry I just unhitched the trailer expecting to move it manually to a storage position. I didn’t check. Lucky for me the little cove only had about 15 feet of water. It took several dives to find it and get a strong enough line on it to winch it out of the water. The only one/ thing hurt that day was my pride. A lesson I’ve never forgotten.
