2007 Nitro SLT 4X4 with TOW package. Weekly pull a 5k trailer with 400# tongue weight. Can't find oem replacement springs. Without trailer rides uncomfortable and bouncy. Thought about coil spring spacers, but I'll still have weak springs. Guess I could add new springs and shocks all the way around. Looked around for a year. Still don't know what I need. We use the Jeep for off-road, but if we do this right the nitro could also be used. Please help...