Joseph,
The horizontal size of your header or footer is determined by the margins
you have. If headers/footers are different on some of your pages most
probably you have different sections in your document (with different margin
settings in them). Or I you have used tabs to align text in your
header/footer the tab settings may differ from one section to the other.
Luc

Headers and footers are section properties. That means they can be different
in different sections. Indeed, many people insert section breaks just to
make them different -- often unnecessarily.
http://word.mvps.org/FAQs/Formatting/WorkWithSections.htm

If they are missing in some parts, perhaps you are using a StyleRef field
that refers to a heading, and also have inserted manual page breaks before
the heading. _When you do that, the page break is a part of the following
parargaph!_ Word tries to put the page break at the top of the header and
what you get is a blank header.

Not sure what you mean by "uneven." Only on odd pages? That, also is a
possible setting.

Formatting of headers and footers is controlled in both the page setup
dialog and in the header and footer styles.

Hope this helps.