The pre-2008 E350 chassis does not come with a rear sway bar of any kind. The front bar is the same one installed on an E150 van, so how good is that one for such an extreme application? If you are a do-it-yourselfer, you could buy heavy duty Helwigs off the internet fairly reasonable. My brother and I installed a rear on his E350 motor home without issues and he was very happy with the improvement. I encouraged him to get a front bar, but he kept his original with worn bushings too.
I went all out spending $3900 from a local specialty shop which makes our 2007 E350 PC chassis handle beautifully. I'll never know if I went overboard, but I can say it was well worth every penny. I had them install both front and rear heavy duty sway bars, rear trac bar, heavy duty front steering stabilizer, all shocks replaced with Koni made-for-motor home, and a front end alignment. What I learned about all this back then, I would do in a particular order to see how little money I could get by with. At an absolute minimum, I strongly advise to get front and rear heavy duty sway bars and a front end alignment, then go from there.
