Here is what I have done. I took out all the old,new,junk parts from the rear bumper area as well as those cabinets behind the rear wheels. The last guy was carrying so much stuff he just didn't need. Things like old starters,batteries etc.. I put all the heavy stuff like sockets and fluids as far forward as possible.
Those big 4D tractor batteries must weigh 120 lbs each and there was 3 of them back there.
It's better. Not 100% but no longer a white knuckle ride. The day I had to drive it a couple hundred miles it was chock full of the other mechanics tools and they were all towards the back.