i am sorry to say but if you have been having these problems for 6 months and you have tried all these things to curb the attitude, YOU are the one not being consistent. you can't expect a discipline strategy to work "consistently" if you don't use it consistently. most likely he knows that if he keeps it up you'll switch tactics, and eventually let him get away with his behavior, so he keeps it up till you do. i am a firm believer in time out. if you spend a couple hours or a day just ON HIM and watching him like a hawk, and time him out when he starts with the attitude, it will teach him that it's not acceptable and he will get out of the habit of going into tantrum mode or whatever it is he's doing. it might be a bit of a rough road getting him used to the idea that this isn't allowed anymore, but it will work.
even now if my son is tired, hungry, or just plain has had a bad day - he might be in time out again, thirty seconds after he got out. but he is a month shy of being 4 and i have never had big issues with his discipline. a few times here or there he has tried to up the ante with his behavior - these rare instances are where i have to up the ante on discipline. i will warn him and then he will get a swat on the bottom. it has probably been months since i've had to do this, i can't even remember the last time to be honest. he is a great kid, and i'm sure your son is awesome as well. for the record, i don't see taking things or privledges or fun acitivities away working with my son, my husband tries it occassionally. the thing that always brings out my son's best side is, plenty of food, plenty of sleep, plenty of excercise and activity, and consistent discipline.