Fast tends to come with practice. Think of learning to write, or to speak a new language. Every word takes a long time. You stumble over words, grammar and the physicalities of forming a sound or moving a pen.
It will be similar with the act of GTD. You need to get used to the mental side, remembering sequences, questions to ask etc, as well as develop some muscle memory. Moving things out of your inbox, filing, writing your lists.
Give yourself time. I read somewhere that it takes 10.000 hours to master a skill. That's a lot of time. Be patient and keep at it. Would it help to maybe have a progress chart? You could track GTD related habits, or simply track the time you spend reviewing and maintaining your lists.
