Yes, check the radius rod bushings where they go through the frame. These
are large bushings. Kinda like(chocholate) donuts. You cant really see if
they are good just by looking at them,most times. They have metal molded
into them,and the metal rusts away.Also, I believe that when a front end
alignment is done, sometimes the large nuts around these bushings are not
retightened. What can happen from either problem, is that the 1 inch hole
where the radius rod goes through the frame ,is made into a  2 inch
hole.The rod and metal sleave can be worn 1/2 way through,making it 2 1/2
inches.The suspension flexes in a way that it is not intentended to.  I had
this problem myself. My 1 year old upper ball joint was bad after 1
year.This on the same side where I had this worn out hole. I loosened the
large outer nut and remembered the number of turns.Then I loosened the
inner nut the same way. Then I removed the outer nut.Do this to retighten
and preserve your alignment. After the outer nut is removed, you can remove
the outer part of the bushing and check it.Chances are that if it is
origional,it is rusted out. This can cause a loosening of the nuts and then
the rod flexes at the frame when the van is accelerater and braked.It
flexes when the van turns too.the Fix is to get new metal filled into the 2
inch hole by welding.$75 /hole in my town.