Itunes shows that I have 2 computers authorized to use itunes and yet when I try to add another unit it says that I already have 5 units authorized already

Your screen shot shows that you have 2 devices associated with your Apple ID.

Devices associated and computer authorized are two different things. See: Authorization vs. association - Apple Community

To authorize another computer, first "Deauthorize all" as described in the excerpt below from Authorize or deauthorize your computer for iTunes Store purchases - Apple Support and then authorize any computers you still have and want to use. Note that authorizations only apply to computers, not iPhones or iPads.

To deauthorize a computer that you don't have access to, you have to deauthorize all of your computers. Then authorize each computer that you have again. You can deauthorize all computers only once a year.

1. Open iTunes.
2. Choose Account > View My Account.
3. Sign in with your Apple ID and password. Forgot your Apple ID?
4. At the top of your Account Information page, go to the Apple ID Summary section.
5. Next to Computer Authorizations, click Deauthorize All.
6. Authorize each computer that you use again.