I is most likely the controller. The rectangular box on your bike. Area13 has the upgraded version giving you a little more power and a new color LCD screen.
Actually, the 35A upgrade controller provides a LOT more power for better hill-climbing torque and acceleration (doesn't affect top speed). On my MiniST2 I max out at about 1,600 watts at full power, over twice the stock unit, although even for demanding uphill climbs the power usually stays around 1,000w or less - I try not to stress the system by using the gears and pedaling.
One thing to note that I just learned recently.... unless the design of these new controllers has changed, you MUST stick with the puny, near-useless, crappy stock headlight, as the controller's headlight circuit can burn out when drawing more than 5 watts; they even warn against the Rad-branded headlight "upgrade" (which really isn't but it draws more power). A very dumb design move for the upgrade, as the stock controller can handle much more power to an upgraded headlight without issue. Annoying, but easily worked around with a handlebar accessory light.