The fact that you stutter more in some scenarios compared to others is a clue - that your sub conscious sees those situations as dangerous and trying to protect you. Why? Because its trained to judge a situation based on how fluently you spoke. So everytime youre in that situation, it reacts with fight, flight or freeze response - thus the trembling lips and other symptoms. So my recommendation is to NOT make fluency as your goal at this stage. Your goal should be presenting yourself as authenticatly as possible... so if you stutter, so be it, do not focus on being fluent. Focus on training your sub conscious that stuutering is no big deal. Your subconscious over time learns NOT to fear these situations.