I too was able to graduate in four years without student debt. I must admit to utilizing the GI Bill for part, a very small part, of my tuition. I also had a 'full time job', which amounted to about 36 hours per week, not counting the week-end employment.
Similar to me. I worked about 36 to 38 hours a week as well, and went primarily to night classes. The small company I worked for was very flexible to help me out with scheduling, but, if I do say so, I did a good job for them in return. I did not have the GI bill (high lottery number) but was able to live "at home" with my folks which helped immensely, perhaps making the difference between you and I in having/not having the GI bill. At any rate, I was prepared by public education for college, and college tuition was affordable, unlike today. (I do remember required books being VERY costly for the day though!).