It might be your pull. It might be your body position. It may be both.
The technique of the entry, the catch, the EVF (early vertical forearm), and the actual pull is key to the propulsion phase of your freestyle stroke. Proper body alignment is important to 1) reduce drag and 2) put the body into a position where you can best generate power.
Some of us are visual learners. Yes, words and explanations are good, but actually seeing your stroke frame by frame is helpful to identify concrete points at which it is breaking down.
I have been videotaping clients and have found the results very helpful in illustrating the concepts that we discuss during the lesson. The clients have been very happy with the results as well. I won't use their visuals here but will use myself as an example as I was recently videotaped. A few things stood out immediately to me as I looked at the frames carefully:
I am on the right. Elbow looks good here and arm directly below my shoulder. On the negative side, I am looking forward too much and my right hand is entering too close to my head. (Note: in the past I tried to have a higher elbow at more of a right angle, which seemed to have injured my shoulder.)
...and here is the subsequent crossover from that incorrect entry.
Another bad habit I have is that my wrist breaks and hand points outward. It should be relaxed and straight.
It looks like I am making good pressure with the right arm and utilizing my back, lats and deltoids. By rolling, reaching and opening up my left hip, I can get more leverage and power.
I offer a videotaping session and analysis for $60. (Please note that these images of me were taken with an ipad. The Go Pro that I now use provides better clarity. I also make sure to get a side view of the client. I unfortunately do not have any side footage of myself.)
If you live in the New England area, please check out my website and call or email me to discuss.