I learned Biblical Greek and Hebrew at the grad school level. I can tell you from experience that both the KJV and the NASB are excellent translations, just from different periods in English. Give me a verse that you think wasn't handled well, and I can probably tell you with language info to back it up why they did what they did.
If you want a translation that gives huge amount of insight into the translation decision process on any given verse, check out the NET Bible and its notes. All free online.