Vietnamese Pronunciation Help
For anyone out there who is struggling with Vietnamese pronunciation, this Wikipedia Article is extremely helpful. In particular, pay attention to the second table, which specifies the IPA pronunciations for all of the Vietnamese consonants in both Northern and Southern Vietnamese.
Another helpful tool is the YouTube channel Learn Vietnamese With Annie. She goes though the pronunciation of all of the vowels, consonants, diphthongs, and tones. Note that she has a Southern Vietnamese accent meaning that she pronounces some sounds slightly different from the Duolingo course (eg. She pronounces "d" as a "y," not a "z.")
Personally, I think the most helpful tool for me has been Google Translate, as it has a text to speech function for Vietnamese. Just copy paste Vietnamese text into the left box, select Vietnamese, and hit the speaker. The translations themselves are also not bad.
Good luck studying Vietnamese!