So, there are lots of things Dipper's name could be. Alex, Roderick, Llamanic/Dominic, or even CrmcrofskElephant2.

But here's a theory I haven't seen anywhere on the internet

In The Time Traveler's Pig, after Mabel helps Dipper she says, "Anytime, Broseph"

My theory: Dipper's name could be Joseph.