Toby is the protagonist. It’s his goal that moves the story forward.
I think the nemesis is First Texas bank as personified by its employees, especially the loan officer at the end. The bank is the one who wants Toby to fail in his goal because that means they get the oil money; the banks are also named in the film as causing the ruin of these small towns.
I think Marcus is Toby’s trickster because for a good chunk of the film, he’s only interested in the chase for the sake of the chase, which might keep him a little further from retirement. He only really becomes invested because Parker is killed; that’s why he goes to visit him at the end, to get some answers. And at that point, his final words are almost those of a mentor. His role seems to shift…hence, trickster.
I don’t know how to classify Tanner and Parker, but they seem to play the same function for their respective partners. Toby/Tanner and Marcus/Parker start out with somewhat antagonistic relationships despite working together, but both Tanner and Marcus are deeply touched by their deaths, and I think there’s a hint of regret in the survivors at what was left unsaid or barely said.