Can I tighten up the steering/handling?
 

I have a 2011 e350 extended with 57000 miles on it. The van drives great, but it does seem to float around quite a bit. It has Continental tires on it E rated I believe and they are inflated correctly to 80 pounds. It just seems like it should hold a line better than it does while driving down the road. Does anyone have any suggestions for shock or suspension changes that could be made that would tighten things up?
Do these things have steering issues I need to be aware of?

Tires, alignment, weight distribution and loading can affect handling.

Something you might consider, with the vehicle wheels on the ground,
If someone moves the steering wheel back and forth while another person looks and checks for any loose movement of all the steering linkage parts. You might see something that way that doesn't show up when the wheels are off the ground.
Sometimes the engine has to be running to get the benefit of the power steering, but I can't recommend this because of the safety liability, hope you understand.