As long as it's in good working order, it's probably not the bike. Those things will go just about as fast as you can pedal 'em. Of course, if your routes are hilly, a lighter bike does help a bit and lower gearing can keep you in a more comfortable cadence for any given speed and out of trouble on hills. But for basic speed on flats or gentle slopes, it's pretty much about how much power you're delivering and how aerodynamically efficient you are. I've got a 1980 31-pound steel clunker and a 2012 20-pounder with thinner tires. It's no surprise that it's a real gruntfest to mash that old clunker up an 8.5% grade for a mile and a half. But somewhat surprisingly, I can make it go within 0.2 mph of what I can do with the lighter, newer model on flats or gentle up-and-down slopes of @ 2% grade. On longer, comfortably-paced rides (15-18 mph) that avoid the really big hills, there's no perceptible difference in effort when on one bike vs. the other. You've just gotta keep plugging away at it and regularly get out of the comfort zone with some harder-paced intervals to get faster. It does get easier the more you work at it.