There are a lot of very good assistance exercises for your deadlifts. Rack pulls at varying height are one of them -- they will get you used to locking out heavier weights. You'll find that as you reduce the ROM, the amount of weight you can lockout will grow significantly.
A few other good deadlift assistance exercises include:
Pulling from blocks (similar to a rack pull)
Deficit Deadlifts (This works the bottom of the pull hard)
Halting Deadlifts (Pull the bottom of the deadlift until about knee height, and then stop and reset)
Deficit Halting Deadlifts
Dumbbell Rows, "Kroc-Style" (aka, take the heaviest weight you think you can row for say 8 reps, and force out 10-15+ reps. Keep rowing that sucker until it falls out of your hand at the bottom of the eccentric.)
Barbell Shrugs (use straps and hit them hard and heavy. If you're not using at LEAST your deadlift 1RM on these, you're not going heavy enough)
One HUGE advantage of partial ROM deadlift training is that it's not nearly as harsh on your CNS as full-range deadlifts are. Once you start getting sufficiently heavy on deadlifts, it takes MORE than a full-week to properly recover from them.
Hope this helps!
"Generally people can't squat because they're lacking in the 'lower ab' area. As in they need to grow a set." - LtL
"No one ever got big or strong by lifting lightweights" - Carl1174
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Valentin Konstantin Platz