Perhaps we do not agree on what "true" is.  I would consider any verifiable statement to be true.  George W. Bush is the President of the United States.  Verifiable.  True.  It has nothing to do with the Bible.  Now if your definition of "truth" means that it must be contained in Scripture, then according to your definition, you are right.  Only your definition is suspect.  Let Webster tell us the definition of "truth": 

         1. Conformity to fact or actuality.
         2. A statement proven to be or accepted as true.
         3. Sincerity; integrity.
         4. Fidelity to an original or standard.

The real danger in your perception of the truth comes in the following steps. 
        
         1. Only the Bible is true. 
         2. I understand it perfectly. 
         3. Here is what it says, and here is what I say it means.

The people who assert the first step usually further assert the next two. 

Perhaps you will surprise me and recognize that we are incapable of perfect comprehension.  How do we get help comprehending God's truth in Scripture if not through the aid of science and history?  Of course we are empowered by the Holy Spirit.  But theologians don't agree.  How could someone yearning to know the truth know which theologians the Holy Spirit talks to and which ones He doesn't? 

There needs to be an impartial yard stick by which to measure, otherwise it is left simply to persuasive oratory.