Then for a 10.4.11 Mac Pro apply the 10.4.11 Intel combo and follow the patient instructions about it rebooting twice. Do this and if it doesn't fix the problem, take it to an expert.
I agree with Satcomer on this last post, update to the 10.4.11 Combo and or back up your system and do a clean install.
I've had sleep issues in the past but with a clean install of 10.4.9 then immediately updating with the above update, i've resolved the issue. If unsuccessful, then yes take it back to the Apple store.