California National Guard put out a 15 minute video with the Chinook crew describing the famous Creek Fire rescue mission. It includes this cool explanation of how they were barely able to gain altitude by cycling between max speed and max engine power.
The CGI he talks about is a gizmo that measures mechanical loads on the rotors, loads increased as they went faster in cruise, redline is supposed to be 120% of design load.
(ignore the diagram at 0:54, they would enter the climb from level flight)