Something that has differentiated Hell on Wheels from similar ensemble dramas has been a lack of clearly antagonistic relationships. Cullen has made friends with almost every character he’s met, regardless of what we know about their motives (see: Durant.) In fact, at this point his only out-and-out enemy at Hell on Wheels is The Swede, and his threat was just neutralized. It may be that the Native Americans represent an ever-present atmospheric danger, but I’m writing only on person-to-person connections.
I was curious what about Cullen’s escape from the boxcar had to do with the flashback he experienced; I would expect more than just a general memory of his wife on the porch to give him the drive necessary to escape, and I’d even hope that the memory itself somehow tied into his actions at the time. Unfortunately, I can’t draw a conclusion with the few episodes we’ve watched so far.