You can do partial rack lockouts on the power rack once every 3 weeks or so. Set the pins so the bar is just 4 - 5 inches below your knees and add a couple of plates each side, cause it's a partial movement and you can lift more than a full ROM deadlift. That will get your body and mind accustomed to the heavier weight. You can even hold at the top for 3 - 5 seconds, which really makes your traps grow. Use a weight that makes you fail at the 4 - 6 rep range.
And every time you deadlift, do one set off the pins, so you're not grabbing the bar all the way from the floor (which is the sticking point for most people). You can probably do 500 for a couple of reps or at least for a slow negative this way. This will also help. Throw in some good mornings and make sure you train your abs and legs hard, cause they help with the lift too.
And finally, don't use a mixed grip all the time. Most powerlifters train with a normal overhand grip and use a mixed grip only a few weeks out of a meet, so they can do it on the day. Use straps too, cause your back is much bigger than your arms and you should never let your arm / grip strength limit your weight.
