You have to switch it up. You can't get caught up calling the same plays over and over. You have to mix it up. If that 3-4 zone blitzing isn't working you definitely need to switch to calling some man blitzes or regular 2 man under coverages. You also have to do some good shifting with your dline and LBs to the area you think the run might go. You have to use strategy. If you continue to struggle you are going to have to lower the CPUs runblocking to help you out.