John:
At first, I would have to agree that the Chama trestle did not have a cable system, but on checking Dorman's Rocky Mt Railroads Vol 2 p50 and 52, there is a bull wheel and cable on the tail of the trestle yet we have pictures of C16's pushing loaded stock cars up it. Another mystery.
The trestle at Sargent had a 6% grade with the main track ascending on a 1.28% grade. This trestle was upgraded to handle the weight of a K37 on at least the trestle portion. On my HOn3 model my k27 can push 2 cars up the grade. A k37 would have no problem with it.
Bob M