It could be the tires or the hubs on your aurora. I don't know what the trek 520 has on it stock. It could be the seat tube angle, crank length something like that. It could be that you're not using the gearing as efficiently, the aurora has larger gears, so are you hanging out in bigger gears and not spinning as efficiently as you do on your 520?

I don't think you should buy a surly long haul trucker without test riding one - because I don't imagine that it's going to be faster than the aurora.

I haven't really ridden an aurora much - I test rode Zen's around a parking lot once, and it seemed like a really nice ride. But I can't say that it felt slower than my surly pacer.