Pith and Gist as synonyms

Pith and gist show as up synonyms on many of the dictionaries. But the gist word is used more often and pith is very rarely used in examples. Can somebody clear me the right usage of both these words.

He watched the trailer but he still did not get the gist of the movie. Can we replace the gist in the above sentece with pith ?

If he did not get the "pith" of the movie, he did not comprehend it's "heart" -- the underlying emotional meaning. If he did not get the "gist" of the movie he didn't comprehend it's plot, or perhaps he missed the point that it was a parody or allegory of some sort.