Just going to throw my two cents in as I can relate to your problem. I was never a huge fan of heavy deadlifts because eventually I would end up hurting my lower back somehow, even though I tried to focus on my form.

I found that the problem wasn't really in my lift, but more in my "returning" the weight back to the ground. When I would work my way up to the heavier sets, the weight would tend to pull me down out of form and this is what would cause the problems.

If you are going heavy you may want to try "controlled dropping" of the weight. Basically instead of lowering the weight slowly and resisting it back to the ground you drop the weight from waist high but follow it down with a loose grip. This makes it so your body isn't resisting the weight on the way down which can pull you out of form. Also, by controlling the weight during the drop it stays where you want it and your ready for the next rep.

This really helped me with my heavy deads and made the exercise alot more enjoyable.