Can't unlock Springfield General Hospital - here's what I've tried so far

It looks like you are stuck here, correct? You can't get Step 13 to start?

13. Hibbert, Krusty, Brockman dine at Gilded Truffle (2 hours each)

Try storing Hibbert's Practice, the original Kwik-E-Mart (if you have more than one), and Channel 6 to reset those characters. After putting them in your inventory you can place them back in your town and hopefully get that task to trigger.