I have a hidden hitch mounted for my Thule 4-bike swing away bike rack. The rear of the car rides TOO low with one adult bike and 3 childrens bikes loaded, and with one suitcase in the rear interior. I had to take the adult bike off to drive safely but the van still is uncomfortably low. (2 suitcases are loaded on the top in my Sears cargo carrier). Is there an airlift I can use to raise it? I have had the suspension checked by the dealer, and nothing is malfunctioning according to them.