High Evangelist Welcome to the board, if you hold a watchtower and Bible up to a witness and ask which is the final authority most will say it is the Bible but in practice they will always put the watchtower first. I knew a JW friend who disputed something in the watchtower he was given that option and when he chose the Bible the elder said wrong answer.
On planet watchtower there is no such thing as true grace. As far as preaching the gospel the JWs think they are ,but you must remember when reading the new testament the general rank and file witness do believe they have a heavenly hope so do not understand the full grace of God. Although most witnesses will try to apply the gospels in their life they all feel they are reading someone elses letter. Because they do not understand the spirit of God.