will a tire like that hold a weight like mine without being stressed very much?
No, it can't. You should switch to something heavy-duty and higher-pressure, such as a Specialized Nimbus or Hemisphere. Then make sure that you keep them pumped up to at least 75 psig!
I cant get into gear 3 major unless I am at 7 minor
What are we talking about here? Music? Constellations?
I am 21 years old, 6'3, and 330 pounds (not nearly as obese as you'd think)
Well, after checking in a book about diet and exercise, you are firmly in the catagory described as
morbidly obese, so don't fool yourself. You are obese.