My 1999 lincoln navigator bounces when driven and the rear is sitting lower on my tires now. Before this happened my check engine light would come on I took it to the shop and they would keep replacing plugs and coils 1 at a time charging me 190.00 a pop and now besides sitting low it feels like powerless and no get up to it and I was told by my mechanic that it probably was my converter? Please help!

Cars & Trucks - Lincoln - Navigator - 2001 Lincoln Navigator