You added straight 40wt oil? Why?
I wouldn't run heavier oil than 10w30 in a daily driver.
Not to insult you, but are you making sure you check the level on completely flat ground? Also, when do you check it? Is the engine cold, warm, just after a long drive?
Your mileage reader essentially turns into instant MPG until you drive enough for it to get a good average reading.
Not sure about the vacuum leak. I don't have that motor.