No i do not need to upgrade my graphics card
you might need to upgrade your graphics card
Oh Thorn, where have you been when we needed awesomeness?

Anyways, first try updating your video card. If you already did that, click
here where theres a website depicting quake 3 tweaks, the link should guide you to a list of download-able configs that would help frame rate issues if you place it in your \base folder (Or try using the website/googling how to tweak your config to suit your needs).
I think I also made a (lame) guide about how to make Tremulous run faster, I doubt it can help you but feel free to take a look
here.
Also, can you give us your PC specs/OS, especially the brand/type of video card you have so we can determine whether or not you really need to upgrade, since Tremulous should run on basically anything (Voodoo 3 and integrated Intel boards should be able to play it).
Finally, if you need
commands, either go
here or
here, both are pretty much the same. You might have noticed some of these commands are Quake 3 based, but Tremulous and Quake 3 use the same engine, so the commands non-specific to Quake 3 would still work on Tremulous.
Also, you said that you averages 80-90 (Assuming you mean) frames per second in a heavily built base, do you know what happened?
Thats all, cheers.