Why do I hit every ball so high?

I belt everything reall high and so my 5 iron only goes 150 yds if I`m lucky, why is this? I take a very shallow divot and I`ve tried putting the ball back and forward in my stance to no avail.

Sounds like a weak, slap rather than a hit.
Try hitting some 3/4 punch shots to make sure that your hands hit the ball before the clubhead does.
Are your divots straight?
If they point left you are hitting across the ball, sending it high and nowhere.

agree with above, my guess is your left wrist (lead wrist) is cupped on impact. left wrist should be flat at impact and right wrist angled. see greg willis right hand drill.

you may be hitting up through the ball rather than down into the back on it.. do you take good divots?

It could be you're releasing the club too early and so scooping up at the ball with the clubhead leading the hands. In that case you need more lag and a later hit meaning your hands lead the club and so the head is more hooded, giving a lower trajectory. Scooping can also result in thins, thicks and tops.

One swing thought I use to help me get more lag and a later release is on the down swing, I try to pull my left thumb back to my left wrist using my right fingers for as long as possible.

This gives much more snap to your hit and the difference feels like flicking your forefinger with your thumb compared to just quickly straightening your finger on its own.

Since I started this I've gained at least a club (and probably a bit more) in distance and so now hit a 6 iron as far as I used to hit a 5 etc.

Another reason you could be hitting high is that your left shoulder is too high on impact. This is sometimes in combination with not moving your weight forward. The more you keep the left shoulder down the lower the ball will go but ideally you should try to maintain the same spine angle as address until your follow through.

I can`t get on with Greg`s right-hand drill, probably because what I`m doing is SO far removed from it!
But I`ve just got the "Greg Norman secret" off Ebay (a gadget that keeps your right wrist cupped) and I`m determined to rebuild my swing along these lines over the winter - although there are parts that I don`t understand still, particularly tha feeling that your right wrist stays cupped ALL the time, on the the follow-through and all? This can`t be right can it?