On memory tests i score well above average. i have difficulty learning new words though. is there any disorder which specifically affects vocab memory?

Learning semantics, : the meaning of words, is a complex task of higher order cognition, as described on http://www.indiana.edu/~hlw/Meaning/learning.html. It may, therefore, be difficult for a person whose neuropsychological function in short-term, active-working & long-term memory is intact. A neuropsychological exam can define the area of impairment.