To deadlift more you have to deadlift more. Try doing the OPPOSITE of what you have been doing. So if that means that you have been doing a couple heavy sets of 5 every week, try doing sets of 8-12 reps for a while and then blast past your former PR. If you have been doing sets of 8-12 for a while try to go heavier and build some rep PRs anywhere from 8 to 1 rep. Any questions? Feel free to ask below.