This line: get_template_part( 'content', 'single-myCPT' )
Will look for a file like this: content-single-myCPT.php
If you’re already using a custom single-myCPT.php file, you might as well copy the code inside content-single.php, and replace this with it:
get_template_part( 'content', 'single' )
get_template_part()
is cool as it allows you to only change the loop – not the entire single.php file. In your case, it’s probably easier to keep everything in one file.