Is changing the font to another Times variant an option? If so, I have a couple of alternatives for you.
Thanks to campa's excellent comments, I have learned that tgtermes uses italics for the header, not a slanted variant (since there apparently is none).
If that doesn't bother you, have a look at the following example:
% Loading tgtermes and newtxmath (in that order!)
% works by inserting italics instead of slanted text
% txfonts also works