xr is time release. So it slowly releases into your system throughout the day. It is made to eleviate the need to take so many pills during the day. And we ADDers forget to take our meds!!
Check with your doctor if it is not working for you.
Were you taking 30mg of IR all at once, or throughout the day? The Adderall XR is equivalent to 30mg by the time it's "done" releasing the meds into your system, so if you were taking 30mg IR all at one time, then you'd need to up your XR dose.
Also, Adderall XR is much smoother than IR....I would almost say that it is "sneaky" in how it starts to work. I can typically tell when both IR and XR kick in, but with the XR, it seems to be a little more gradual.