Couple of things come to mind.
1) The Speed Pro has an SRAM Dual Drive. When you are not in the 1:1 range of the dual drive you will take a small, but real, efficiency hit. I recall that the middle range of the dual drive is 1:1. So, if when hitting a hill you shift into the low range, you suddenly will be faced with that additional power drain.
2) User error. I seem to fumble the shifts at the beginning of steep hills more on my folder than on my big wheel bike. I don't know why. If, like me, on a particular bike, you screw up the shifts, then you would percieve yourself slowing more than you usually would. Once I get moving up hills I get organized and in the right gear, but there is definitely a wall effect at the bottom of steep hills.
Speedo