What is the ruling on the tongue slipping to the articulation point of a letter when pronouncing it in prayer and outside of prayer, while the letter is audibly pronounced correctly?

It appears that what you refer to as a "slip of the tongue" from the letter's articulation point is merely a form of [waswasah] (whispers from Satan), especially since the examples you mentioned (lam and fa) are unlikely to involve such a slip at their articulation points. The letter lam is articulated from the tip of the tongue adhering to its point of articulation without slipping, and the letter fa is articulated from the lips and has no connection to the tongue. These whispers are from the deception of Satan. Ibn al-Jawzi mentioned that Iblis deceives those performing prayers regarding the articulation points of letters, causing them to exaggerate to the point of departing from proper recitation and distracting them from understanding the recitation. Therefore, it is advisable to disregard these whispers and pay no attention to them.