Yes - I have those issues as well - if I read, its ok, but if I speak just without having the words already, I get monotonous because my voice just stays in a relaxed mode while I am trying to find the words. In the worst case I have breaks or even "hmm, emmm" sounds in between. Forming the sentences in the head before speaking is a good advice, but I think it is not easy to always follow it and takes some getting used to. But I believe if it works, it gives a better speaking voice.