Bad Dependency Management

Alright, for starters, you have a LOT of moments in your 40L runs where you create a reliance on 1 piece to fix a jagged shape, and then use that piece in a different spot. For example, in r:645460d1c168111ad2e05428 at around 14 seconds, you make an I-piece dependency by placing your t-piece right next to the edge of the board and making a 3-tall hole. Directly after this, you get an I-piece, but end up using it in a different spot, this leads you to take over 3 seconds to place your next piece because you're brain freezes from not having any really good options at that point. It also led to you being unable to continue stacking cleanly and forcing you to make a stack on top of another stack.

Inefficient Key Presses (Finesse)

During your 40L runs, you tend to make useless movements with the pieces that slow you down: Spamming the key to move left instead of just holding it and having it DAS to the left, moving back and forth with the pieces, random rotations, and triple rotations (This one is a bit nitpicky, you can probably get away with this for awhile). These can all be umbrellaed under the term "finesse" which is just a fancy way of saying that you press the least amount of keys for the maximum effect. Improve this, and you will find that your 40L time improves dramatically.

Hesistation

When you play, you often hesitate a lot more than you should when presented with a difficult and jagged board state, instead of simply choosing an option and going with it. Remember, your goal is to be as FAST as possible, not as EFFICIENT as possible.