Lets start simple first.
Is your fluid level correct? Top up.
Is your fluid old or thin or dark from carbon (burnt fluid)? If your transmission has been neglected, try a drain and fill method every two weeks until the transmission fluid is clear. If well maintained, try a flush.
If problem still exists after the above, it may likely be due to a worn valve body.
http://www.transmissionspecialty.com/parts/DM/CD4E.htmThe link above from Sonnax, details a list of products they offer which make improvements over the Ford parts. I suggest you download, save and review all the pdf files about their various CD4E products.
Under the shift concern section...
(Bump in 2nd or 4th, soft or harsh shifts) (2-4 Accumulator Piston) (73840-24)
That may be your issue. A rebuilt valve body using Sonnax parts can be had from Axiom Automotive Technologies.
www.axiom.com ($300 plus shipping with no core). In my opinion, this is better than a Ford rebuilt unit.
Should the valve body not be the issue, you still need the new valve body if a rebuild is needed.
