Double heading down grade

It was my understanding that there was no need to double down hill, plus there are weight restrictions that also prevent this.
One K-36 or K-37 could supply enough air to take 70 cars down from Cumbres to Alamosa, the weight restriction over Cascade trestle would also prevent doubling. For Chama turns this is also the reason for not doubling down to fetch the second turn, Lobato Trestle. The Helper crew to Alamosa would be cut out light and be forced to earn a lower rate of pay. (Can anyone confirm the lower rate of pay?)
Double heading from Durango to Chama was done even though there are some down hill run in both directions because they had up and down grades along the line. Doubling was preferred to Mid-Train Helpers to minimize the slack action and prevent derailments
Kevin