Matt,

When you are straight and level, the speed of the plane increases to it's maximum and would not normally drop off unless you lower the throttle, but when climbing, the plane starts to slow down though you may remain at full throttle. The torque really is not changing much in this example but it is changing as the load on the engine is slowing down the rpm, so if anything the torque and it's effect is getting stronger since most times we prop for top rpm but usually top rpm is beyond the torque curve of the engine, but the speed of the plane is slowing and as such, the torque "effect" becomes more pronounced since the plane is slowing and the engine is getting into it's torque curve. Most engines make their most amount of torque well below the max rpm it can achieve and as such the torque curve actually may drop off a bit once you get past it's peak.

I'd think of it in terms of effect based on speed/throttle position and prop rpm, sooner or later the speed has slowed enough that torque starts to pull the nose to the left and the prop wash starts to push the tail to the right, hence moving the nose to the left so the slower you get going up the more you have acting against you.

A good way to see this is to not do anything on the trim chart. Go fly and pull a vertical line and correct the flight path with whatever amount of right rudder you need. Once you have some rudder in, just chop throttle but do not let go of the rudder. Guess what's gonna happen, the nose will straighten out and depending on how much speed you have when you do this, it might even go to the right a fair amount because of the rudder.

When I do thrust changes, I will fly vertical lines and use my rudder trim to get it tracking straight up for about 500 feet. I will leave the trim in and land. I will then use a protractor to see how many degrees the rudder is from center, divide by two and use that number for the amount of engine thrust I need. It usually gets me very close if not right on the money. Mind you, you can never get the plane to track perfectly straight all the way up until the engine can no longer pull the weight, which on a seriously overpowered plane, can easily take you past the point where you cannot even tell what it's doing so it's best to do it to the normal height that you would normally do a hammer head/stall turn and for me it's about 500 feet

The book actually does a much better job at explaining it than I have