I ran some more tests! I checked my 50mm 1.8 II and my 15-85 and they both seem to focus just fine, which makes me think again it could be the lens itself. What I don't get then, is why it seems to work just fine on the 600D and not on my 550D. I'm actually hoping it's the lens, so I can just exchange it without having my camera in a repair center for a month.
Any thoughts or advice on this issue?
Sorry guys! Just saw I'm writing in the Sample Photo topic, I will redirect my question on the normal lens forum!