something that works for me in any stroke is to have my arm relatively relaxed throughout extension only puting "some" muscle at the very end of the movement.
I consciously rotate my humerus externally which helps me further protracting my scapula and elevating one side of the rib cage (internal rotatio got me to bind my spine an imho is a healthy spot to start the motion which further internally rotate the arm). Once I'm "here" I've pretty much nowhere to o but to "fall' into the catch.
the release of tension in the overall shoulder is all the strength I need for the catch.
As for motivation, I believe that it is part of the learning to get it and lose it.
It happens to me all the time, I start to think I'm doing right then discover a better way or a mistake of some sort. I correct it or try and all of the suden my stroke breaks. Soon after I usually avoid speeding to if not consolidate (more on that later) but erase or replace the old (early) habit.
I tink it is good news, I do not want my swim to consolidate too much while it is still plagued by glaring issue. It is seems you are in a pretty flexible spot.
Some people are pretty consistant, ad they consolidate a stroke fast and find it extremely hard to alter. They are used to do volume and given speed, significant changes are almost out of the windows. When I still feel a little down, I look at some people in a "relaxed" club that pretty much make no sensible progres and to me it seems they are swimming significant slower than their level of fitness allows (dam I wish I were that fit, balanced, etc.).
Many will disagree but I would advice to pass as much as possible on tools, especially fins. Learning as its up and down at least wrt the observable short or mid term results, if you like what you are doing keep pushing through, swimming as many sides which will complement whatever you do in freestyle.
Fins and what not, might be useful if used properly. What I see at the pool is pretty a hack and a way to deal with delayed satisfaction. I especially do not believe in the slightest that it helps finding out to kick... in the slightest...
The foot actions are critical. Foot flexion and extension, properly lead by the big toe hence resulting by the use of the proper cinetic (muscles). It is not the case for lots of people (mostly our fucked up shoes shapes). I noticed that lots of good swimmers that migh have practice like forever have wide and healthy foot. The foot actions result in the action of muscles mostly extrinsic yet how cann you feel it with your feet encased in the pretty unflexible toe box of fins?
As for me during my last swim I could not really get into freestyle no matter it felt great in my previous swim. I did not feel like push through it or force it. I spent most of my time doing backstroke and sometime doing "grueling" core training in breaststroke. My streamline is OK but not healthy. My spine is rotated. I work to keep to resisting rotation when I extended forward, during the leg recovery as well as during the kick. There are various muscles, with different strength none of which are bother by my spine position not that willing to pay attention to it either. I stick to it. Breaststroke is my best stroke though at the moment I'm slighty slower than I used to. I don't want to do the same mistakes, detrimetal to my health, that I did unknowingly before, I'm also sure that when I find a proper line I will faster. It keeps me going.
Anyway, have a good one you guys, I would back be in the water soon :)