I do a 2-part pull, not the 4-part catch/wrestle/wrap/throw.
After my hand enters, I relax the shoulder, letting the elbow drop down and the forearm to drop back by allowing the shoulder to rotate (you can make this passive, by allowing the water to drive the hand back, or make it more active by adding a little pressure but not changing the mechanics) -- this is analogous to the catch in freestyle.
Step 2 is to pull. I have found that if I have my arm in the "correct" position it is superfluous to think of wrestle/wrap/throw as 3 separate actions.
2 sources of strain:
if my tricep is overactive in extending the arm as I do step 1.
If my biceps don't relax as I do step 2.
My biggest problems now:
Keeping my hips from dropping as I pull. It seems like as I pull down I want to kink in the middle.
Kicking: I find it hard to maintain a steady 6 beat kick. I just let the legs do what they want to do, which is a little more active than a 2-beat kick. I think it is necessary to do a more active kick than freestyle in order to get a little higher in the water. But I have trouble maintaining it consistently.