When you say the problem is you, what do you mean by that?
It doesn't sound like a lack of knowledge, so why does it take longer than expected for you to complete a task?
Is it the kind of task that can be broken down into steps? If so, can you isolate the steps that are taking too long?
Is is a task where you could be doing different things at the same time, like having a CNC machine run while you set up the next part of the job?
I would focus more on doing it right than doing it faster. Speaking from 25 years in the software business, I would rather have something done right a day late than done wrong a day early. The stuff that's wrong eventually has to be fixed, and then nobody cares that it was done early.
If you don't have any luck figuring out what's not working for you, maybe you could ask someone more experienced, or who does things faster, to take some time to watch you work for a while, and maybe they can tell you what they do differently.