We're talking two different things here. On long decending grades the helpers ran light ahead of the train. On the roller coaster profile between Chama and Durango they ran doubleheaded all the way until after the Bocea Hill wreck in 1958. After that, one engine handled the train from Chama to Gato. the doubleheaded to near Falfa, then one engine brought it down the hill to Durango. Both the decending grades in this case were 2%.
To comment on a couple of above things -
There are only a couple of short grades between High Bridge and Tank Creek. One engine can pull the train through this stretch.
There was no difference in pay between helper and road engines (at least on the ALA-DUR line). If running light, a helper crew got $1 a day extra for lining thier own switches. If the road crew did a certain amount of on-line switching, they got paid "local rate" (which was less than $1/mile) for the day. The main difference in pay was the helper made faster running time and the crew got less overtime.