@Jackspratt2 If the backend is dropping under load you are under sprung for the weight or overloaded, this is not rocket science. You will note I started a post on transporting an engine in my Disco, to avoid possible overload.

One of the solutions that is common is to put a good set of springs in the rear, and then add air bag helper to level when required. This allows you to put appropriate springs in for the the expected load with air bags to help level.

Link below, you would need a switchable air compressor

https://www.etrailer.com/Vehicle-Sus...one/F4121.html