If your steering box is adjusted too tight, it will absolutely affect center return. And it's pretty easy to get it too tight.

If the steering box is just right, or a tad loose, return to center should be fine.

Since you monkeyed with it, I'd loosen it up. See if that helps. It's a good diagnostic measure, if nothing else.

You had an alignment done. Did you look at shims? New ones will be shiny. Old ones, black/gray from living under the hood... Just look for evidence that they checked them out.
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-Matt I ♥ my ♂