I also had this problem. I'm not quite your size (I'm 6'2 and 220) but hopefully your problem is as fix as mine was.
An 8 iron for me would go about 140 yards max but with a big ballooning trajectory that was killed if there was any wind. This was very frustrating as playing partners who I would outdrive by 40 yards would be taking a club less than me when hitting
irons.
I noticed that when I hit the ball, although it would go pretty straight with just a hint of fade, the marks on the bottom of the club face would indicate that I hit the ball with the club face wide open! I wasn't hitting a slice with this open face as my swing path was quite in-to-out to compensate. So I was effectively turning my 8 iron into a sand wedge!
I really noticed this when I had a video lesson which showed this open face at impact. This cause and cure were very simple. My grip, which I thought was quite neutral/slightly strong was actually very weak although it didn't appear to be at first glance. Making my grip than bit stronger has literally changed my ball flight. 8
irons go about 160+ with a slight draw and I've lost my tendency to fade my longer
irons too.
I would recommend a video lesson to pinpoint what you are doing at impact as it's very revealing.
Moving the ball back a fraction can also be a help as CM44 has mentioned (I also play 7 iron dead centre and everything else moves back and forward from there).