I bought the car from CarMax, not a Hyundai dealership.
I bought the car under the Air Check program in Texas. The program targets getting older less efficient cars off the roads. They give the authorized dealer money to crush your old car and not resell it. Thus part of my upset in not getting better mileage.
I really appreciate all of your input! All is very useful information, actually much more than I anticipated! Should I find out anything definitive, I will let you know. I appreciate the information on the synthetic oil as I have never dealt with it and didn’t know much.
And “oldschool”, you are right! I do not feel old!