NEAPCO is a USA company that makes u-joints. Many of the u-joints sold by Advance Auto parts, Car Quest and others are reboxed NEAPCO ones.
When I did u-joints recently, the first ones I got where too small across even though the cap diameter was right. So it sounds like I had the opposite problem.
The first caps I had which were too small, IIRC were a 2-0053 NEAPCO number or whatever the CarQuest number was for that joint was. I went and got some 2-0054 u-joints which were the same cap diameter, but were larger across.
So I suspect what you got were a 2-0054 or equivalent, but need a 2-0053. This all makes sense since Superduty trucks with the 7.3 began using a larger u-joint than the OBS trucks did.
If you'd like, you can look up your u-joint part number here in the
NEAPCO U-Joint Catalog.