I went over in my mind that night what was I possibly doing wrong, going over the movement in my mind. Then it occured to me: I was supposed to 'get tight' before I began the lift, as in tense my abs, my glutes, grip the bar as hard as I can and tense my........lats?!!! That was it. I wasn't tensing my lats before I began the lift. So I went back and attacked the 480# loaded bar with pre-tensed lats and sure enough, I was able to pull all 5 reps with much more ease.
Tense these to increase your strength
So, long and short, if you are missing deadlifts, it doesn't hurt to check if you are tensing all the right areas to get maximum strength out of your body.