Hello there, long time lurker, first time poster.
I too was glitched on this achievement. So I did what Demon said, started over. I have a 360s and saved the new game to my console memory, used codes to unlock characters, and did free play after every level. It popped as I got the last kit on Zillo beast. I don't know if it had anything to do with it, but this time I did not do the hidden levels on the Invisible Hand. I did all of the Republic missions first. So just another wrench to throw in the system if you still have issues.