Is the King James Bible the only true Word of God?

No. Some people are so fanatical about the exclusive "truth" of the KJV that they would doubt your salvation if you were saved by reading another version. The New International Version Bible is probably the most attacked of all the modernized versions, but any errors it might contain are subtle ones.   Other folks believe other translations are the Mark of the Beast.

There are some problems with the KJV, slight translation errors. For example, the word "God" in Daniel 11:37 reads, "Neither shall he regard the God of fathers," thus referring it to Israel's one God but as some of the new translations have, corrected that version to the: "gods" of his fathers referring to the Roman pantheon of many gods. The American Standard Bible is preferred by many Bible teachers, and the Standard American 1901 Revised Version of the Bible (translated from the original tongues) and is a very reliable version, although harder to find all the time as the Christian publishing industry has become more commercialized.

Some fringe groups have produced translations that are very harmful to the true Gospel message, but I believe the real doctrinal train wrecks come when people misinterpret the Bible. I primarily use the KJV, but I don't make a religion out of my choice.