Hi mart,
Mine was an acoustic nueroma, but I also had some diction problems. After talking with my choir directors, I decided to go back to basics. For an hour each night, I worked through vowel sounds and the tougher consonant sounds. I would then sing through my songs, and if I noticed I sounded off on a certain note or letter sound, or if something rubbed me wrong, I'd practice that letter and note over and over again. I did this in the car, at my apartment, everywhere. I'd also sing for someone who had music training and ask their advice, then take their corrections.
My choir is just for fun, although it is a class, but I used it as my speech therapy. However, if your are still struggling speech therapy would be another option as there would be someone there to tell you exactly what sounds need work, and why, and the best way to do it.
Best if luck!
Kristin