Here's my theory, Paul, speaking as a complete non-expert!
It sounds as if you're sharpening a huge image and then zooming out to view it at smaller dimensions. That way, it's bound to lose its apparent sharpness, because it was sharpened at what is now below pixel level.
If you want it to look like your old pictures, surely you need to resize it first, to viewing dimensions, and then sharpen it.
Guy