I just purchased a used legend 2place inline enclosed aluminum trailer. My 2011 f150 with the 5.0 V-8 pulls it just fine, the problem is, it causes way too much sag in the rear of the truck. (About 3" with both sleds in it) Has anyone else run into this pulling a inline with a 1/2 ton truck? If so how did you remedy it? Air bags, helper springs, add a leaf? The trailer with the both sleds is only about 4000#. Thanks for your assistance......