I have my excerpt length set at 100 words and they show properly on the home page, but on author or category pages the excerpts are 55 words in length. Any ideas how to get them all to show 100 length..?

what version?
plaese attach an export of your settings (ato->export/import settings)

Version 3.5.1

Now the front page has reverted to 55 also. My excerpt is set for 100 words.

Attached file.

there were a number of issues with excerpts in the 3.5.x versions. I'd suggest you upgrade to 3.7.3 to see if it is still an issue

Upgrading conflicts with important plugins at this time so I cannot.

Well you could make sure you have all the bugfix's for 3.5.1 applied
I just tried it in 3.5.1 and see the issue and then switched to 3.7.3 and it works fine.

Originally Posted by ARealpolitik

Upgrading conflicts with important plugins at this time so I cannot.

Upgrading the theme should have no impact on plugins and if you do a manual upgrade you could just switch back to your current version should there be any issues.