Double check that you have the leaf spring pin in the alignment hole of the lower plate.
I accidentally had one misaligned when I redid my leaf springs a few years ago.
I noticed it when I tightened the nuts on the u-bolt (beneath the lower plate)and it seemed to bow more than the other side before it got tight.
The pin wasn't in the hole!
I took off the plate and had a local machine shop use a press to get it flat again.
I was much more careful the second time I assembled it.
Hope it's that simple!