Besides the EGR block plate, what else has been done to the engine? Tuning type, fuel system mods, air intake mods? Any wiring harnesses disconnected when you installed the blocker plate?
The valves won't need reajusted unless extreme strain has been put on the motor due to high rpm's. The LBZ can handle some pretty nasty rpm's.
A dirty MAF might be a problem but without more info, it's gonna be hard to help.