zulu, since my max is about the same as yours, here's what i do..
bar x 5
135 x 5
225 x 3
10 reps on hyper extension to warm up my lower back more
275 x 1
stretch a bit(cause my left hamstring gets tight no matter what)
315 x 1
335 x 1 (PR)
like cubanito said, you raely have to stay tight when you do it (i dont and that my problem besides my hips).
also, if youc ouldnt get it off the ground, try deadlifting off a 3 " block just to see if you could've locked it out so your not totally discouraged.
last week when was deadlifting, i did my wawrm ups, and did 315 x 3, and then went to 335 totry and get 2 or 3.. .and i only got it up half way and couldnt get it past there.... i couldnt get it up cause i was too tired from 315 x 3, so im thinking that maybe you tired yourself out from doin something before you went for your max