My husband told me that there is a filter in our drip coffee pot that I should remove before I run it through the clean cycle, especially when I add vinegar. Why? I have no idea, he's the one that pays attention to all the techie details and owner's manuals

. Could the filter be your problem? I think you're supposed to change the filters every so often also. Maybe that will help with the taste issue.
Could you have possibly bumped the setting for the the heat element at some point and accidentally turned it down? If that isn't the problem how old is it? Perhaps it's wearing out.
Good luck!