serious...
I believe the source you quote is a bit misleading in the differences between the KJV and the NKJV with the other best modern translations. I am no defender of the KJV (or NKJV), having stated here many times my preference for the NASB for serious study of Scripture because is is closest to a word for word translation, but I have consulted both over the years (along with the NIV) and have found few "serious" differences in meaning, once you take into account the changes in the English language over the centuries.
In either translation, when in doubt, one should break out the Greek/english text and do a greek word study using a good lexicon. The same is true for using a Hebrew lexicon for the Old Testament and both will have sections to handle the Aramaic involved.
mlsoft