google user agent and cloaking

I'm trying to step away from using "read more" sections but want to keep the content read by Google. If I were to send Google user-agent to an html page that shows all the content, and send users to an html page that shows the read more section, would that be considered cloaking?

Yes it would.

Also, user agent detection is not effective long term since Google and all the major ad networks and search engines employ additional shadow bots, partners, and manual inspectors to look at pages. In all these cases you won't have a match with the UA.