Shaking/Shuddering while towing trailer

thanks for the help! i can tell there's several hundred pounds of force on the hitch (from two of trying to deadlift it!), and the chains take a decent amount of muscle to get into place, using the pry bar. If it were any harder to lift them I think the average person wouldn't be able to do it without working really hard.

When I kick the bar/chain they don't budge, for what that's worth.