MattC,
Just a (couple) point(s) on the deads... (from a guy who turned his from a weak lift to a strong one).
-don't ever let your back round
-maintain an "arched" back
-if the arch deteriorates, allow the back to straighten... but drop the weight at the first sign of rounding
-keep your butt lower, drive with the legs
-let your knees move out over your big toe
-don't "snap" at the weight, pull it. (snapping 400 lbs tears tendons, elbows never recover)
-lead up with your chin and keep your chest inflated
-keep the bar as close to the shins/legs/body as is practical
Most importantly of all:
-Don't ever lean back beyond the perpendicular upright standing position
...it's a waste of energy, works no muscles to any great extent, endangers the lower lumbar region by introducing excessive sheer forces in an unnatural position... and... not meaning anything derogatory here... leaning back is actually a method of finishing a deadlift that has finished in a "hitched" position. Look deep, deep-down into your heart of hearts... you know this to be true.
Hitching is considered cheating in powerlifting, in bodybuilding... leaning should be considered hitching, and by definition a form of cheating.
Hope this helps, the only other advice I could offer would be to decrease your height; widen the shoulders and ribcage; maybe shorten your legs... it works. I'm 5'4'' 210 lbs (a chubby 25% bf) yet I can deadlift 405 for 5 (405 for 10 if I allow my back to straighten). I'm not strong, it's all leverage and proportions.
The Luke