it probably is rotors then..... your tires may have a small problem that is more evident at slow speeds... I had a car once that was fine until 70, then it would vibrate (mud/dirt inside the tire was the cause for this one).... However, the slow speed stuff is probably a small tire issue or you're just paranoid like me.... the braking problem does sound like rotors.... I think an inspection (if you don't want to do it yourself) is like $20.00 at most dealers/brake shops