Hi! I also have a stutter and struggle with words with vowels. I have two tips that may help. The first one is to start quieter on the vowel part of the word and then get louder once you get past it. For example, it may help to start the "ah" sound in "appreciate" lower and then basically swing your voice into the "ppreciate" part. Moving your head slightly as you speak (I guess like swinging your head forward slightly) can also help here. Secondly, I would try linking it to the word before. I have done this many times - like if saying "that joke is inappropriate," I would say "that joke is-sinappropriate." So the word isn't necessarily starting with a vowel - it's starting with an "s." Just thinking about it that way may take away some of the stress! Hope this helps :)