There seem to be multiple definitions of the pulls going around, so it makes it hard to know which you're talking about. I'm guessing, from your question, that you're referring to the pull from knees to upper thigh/hips?
Don't pull the weight with your traps at all. It should be more like you pull yourself with your traps. The way I look at it, is the "shrug" and the "elbows high and outside/back" portion of the lift is not to elevate the bar. Instead, when you start these shoulder/arm movements, you should have already hit your finish, and you are in the process of jumping your feet into the squat stance. Effectively, you have virtually no resistance pressing against the ground, thus the shrug and elbow bend is being use to pull your body down under, and to, the bar.
Something that I do to remind myself not to pull with the arms are clean pulls. Or sometimes a complex of like pull + pull + clean. I don't know if that's a standard coaching technique, but it seems to work for me to get the feel of leaving my arms relaxed through the finish. Maybe give it a shot?
I agree with Thomas and his description of the actions your body is conducting at that time and the cues that go with it. They're all used to get your body under the bar. This needs to be a vigorous pull under, maybe just as vigorous (if not more) as your second pull.
I would add that you never want to pull with your back, either. The drive should be generated from actively pushing against the ground, as if you're trying to drive your feet through the ground. Granted, a strong core/trunk is essential for a balanced pull and receiving position, but the majority of the height you get from the bar is through your leg strength/extension and the power it generates into your hips as they extend as well. Don't simply "open" your hips; rather, simply focus on always pushing against that ground and the hips will have no choice but to extend fully.
As for movements to help, again, I agree with Thomas. In addition to the pull + clean, you might want to work on tall cleans to understand what we mean in regards to what your traps and arms should be doing. From there, work down the legs at different heights (mid-thigh, knees, below knees) in hang positions.
The weight you'll use for the tall clean will presumably be A LOT lighter than you will be able to pull. While I don't think that a pull + tall clean complex will help you develop strength, you will be able to use the opportunity to beat proper technique into your muscle memory as you bring the bar up to your starting position for your tall clean (or snatch). Unless you're taking the bar off a set of blocks, you're going to have to pull the weight up. The trick to working portions of the lifts is to not forget how to perform the rest of the lift (naturally, performing the entire lift in a fluid motion falls into this category, too), therefore, it is in your best interest to practice taking the bar off the ground properly at all times.
I recommend taking the opportunity to practice your set up and technique at that point. However, like I said, you're not going to get much strength gains from it. For that, you should be doing heavy pulls apart from this exercise.
Lastly, your English is very good -- don't discredit yourself! Happy New Year to you and yours as well.