How does a train climb uphill? Our commuter train, in rain, couldn't ascend yet other trains whizzed past us.?

The ascent is such a gradual incline over a number of miles - 20 ft above lake level (start) .. to approx 700 ft above lake level (8 miles later) but we "couldn't" make it and were sent back to "lake level" to board another train. Is there something in the wheel system which grips the track which wasn't working? It was only raining and the temps were probably in the mid 40's.