Yes, barrel will need cleaning at least once every tin. However if you do a really enthusiastic clean - like using a pull-through that needs all your strength to get it out of the barrel (!) - then be prepared to use fifty shots or so to get it to group.
The EV2 has a probe to seat the pellet but this does not make it immune to changes in how you load the pellet into the breech. If you are not consistent here you will get looser groups.
If in doubt, try a smaller head size pellet. Bismags are tight in mine and don't group at all well. JSB 4.52's are normally its best diet, depending on the batch, but sometimes I will get marginally better groups with 4.51's.
Finally, a mechanical check. Is the grub screw that holds the muzzle brake onto the front collar properly tight? This has a point on the end of it that sits in a vee groove cut in the support stud.
PS what's the build date? The firing valve was altered at the beginning of 2005 and AA were doing a free upgrade when the early rifles went in for service or repair. The new valve is much more consistent and uses a lot less air per shot.
Rich