now here is my issue: alot of the time, he is just fine with stepping up onto my hand. he is always good with coming out and going back into the cage. the problem arises NOT ALL THE TIME but SOMETIMES when he is on an object outside of the cage eg. bench, lounge, tabletop, human head
and i try to get him to step up off it onto my finger. his eyes will pin and he will bite hard at my finger, drawing blood half the time! until i can eventually get him on my finger and then he is fine again? i've noticed it mainly occurs when trying to get him off high places like tops of bookshelfs, cupboard doors, my cockatiel cage top and especially peoples heads-which despite all our encouragement to the contrary he loves to do.
Building on what others have said, I think at these times your bird prefers to stay where he is over to step to your hand. You must accept, fundamentally, that your bird has preferences as well as instincts. At these times, when you ask him to step to the hand, you are asking him to give up something he prefers and, possibly, to move to a place of decreased security just because you prefer something else. At such a time there's not much in it for him. If you then miss or ignore his pre-bite signals and persist in requiring him to step to the hand, he may feel forced to escalate to biting. Understanding that I'm not there to see it happen, I still strongly feel this is at the root of what you're experiencing.
Understanding this concept that your bird has preferences as well as instincts which he must obey, you are placed at a crossroad. You may follow your current course of sometimes disregarding his needs in favour of guiding his activities to accommodate your preferences, or you may form a strategy that helps you get what you want while simultaneously accommodating what Birdie wants. While you are considering this, please also note that as your bird matures he may become less willing to accommodate the intimate handling he now allows. It would be in your very best interests to note his discomfort signals (such as the eyes pinning and probably some change in the way the feathers are held about the neck and head) and to respect his objections (such as that "occasional squawked complaint" you mentioned) as well as rewarding him heavily when he is happy to comply. In this way you might ward off an escalation in your problems.
One of my favourite training tools is that of teaching a behaviour that is incompatible with and preferable to the behaviour you don't like. An easy example of this would be for a dog who jumps up and puts his feet on your guests. You train (condition) the dog to sit on command, every time you command, and to remain sitting until you release him. Then, when guests arrive, you simply ask the dog to sit. He cannot sit and jump at the same time. The reliability of this trick is dependent on how well you trained your dog.
For the bird who doesn't want to step to your hand in certain situations, I would suggest training him to fly to your hand (or some designated spot) upon command. You should train (condition) him well using positive reinforcement. He will come to you when what you offer is more rewarding than what he has.
For the bird on the head, how lovely would it be if, as your bird prepares to fly to someone's head, you could simply say "Birdie! Go Home!" and thus divert him to fly to his cage instead. Wouldn't that be nice? Or, maybe you could instead call him "Birdie! Over here!" as you hold up your hand for him to land on. Maybe you would prefer him to fly to a place you indicate by pointing instead, as "Birdie! Go there!"
I hear you saying that's a lot of work and you need results right now. Consider that the head is an attractive spot due to its relative height and easily gripped surface. If you lower the head and raise the arm, there is a fair chance Birdie will adjust his preference accordingly, especially if the hand holds a treat and is easy to land on. Before my bird learned to fly to my hand, he did want to land on my head. I allowed this initially because, hey, he was flying to me of his own choice. It would be counterproductive to discourage such an overture. However, once the bird learned to be on the hand (actually, the wrist), I discouraged head landing by quickly stooping down as he tried to come in for the landing. However, at the same time, I strongly encouraged him to fly to the hand. Now my bird never lands on my head, and he usually flies to my hand upon invitation. I am sure his hand-landing compliance would increase if I cared enough to practice it more. It should be noted that I try to be at least a little aware of what Birdie's up to, and so am frequently forewarned when he is thinking of coming to me, and I hold out my hand to make the choice easy.
I hope I've given you some thoughts to consider that will help you solve your problem. Simply recognizing that your bird has preferences and will make choices is a fundamental step. Realizing that you can make the "right choice" the bird's desired choice depending on how you present it is another.
but he doesn't try to bite) he has unclipped wings but i do trim his toenails, and he lets me do that very easily (sits on my hand while i clip them) knows how to step up and is currently doing some harness training.
i thought maybe it could be a form of bluffing but i don't know... 
