Might be more than just pressing them right.
Might be your bearings aren't correct to start with.
Did you compare each set side by side new and old? I wonder if a new set is taller/thicker than one of the old, or perhaps both are?
You can probably check this after the fact from the numbers and the assembled bearing specs in the catalog.
http://www.timken.com/en-us/products/pages/catalogs.aspxGrigg
