What does the phrase "like a pig going for truffles" represent? Persistence?

Answer 1

Yes, persistence -- with "tunnel vision" in a way -- not looking right or left, just straight for the truffles and nothing else!

There is also the interesting juxtaposition of putting "pig" in the same phrase with "truffles" since pigs are supposed to be messy and sloppy and truffles are very expensive and difficult to find.
http://www.herbarium.usu.edu/fungi/FunFacts/Truffind.htm

http://www.stuartstories.com/stories/ruffino.html

http://www.amateurgourmet.com/2006/12/some_eat_like_a.html

!!

Answer 2

In some places, pigs are used to search for truffles. They love to eat them so they are used to root them out of the groung.