Are you changing the tone to "Work Hard"?. I have a sim in the culinary career, and she got the first few promotions in one day - I had her Very Inspired with the daily task and the level tasks completed. As soon as she left for work, I changed her to Work Hard. After the first few promotions, it's been taking longer. Also, I had her husband on another lot and got busy with him and forgot to change the tone to Work Hard a couple of times - she made very little progress on those days, even though she went to work Very Inspired. Now she's at level 6 and went to work Inspired 2 days, I changed the tone to Work Hard shortly after she left, daily and level tasks were completed, and it still took 3 days to get the promotion.
So I think Work Normal makes progress, but slowly; Work Hard makes faster progress, but may not be enough to get a promotion in one day. I think everything else lowers performance. And maybe overall promotions are just harder to get than in TS3.