Deadlifting at 300

I weigh 161 and right now my deadlift is stuck at 300. I workout every five days I'll go 5x5 with 315, then one heavy single (300/310), sumo deads x5 with 260, then the same with 225. After that I normally go knock out my upper and middle back stuff, then I do 5x10 hyper extensions with just a 20lb. dumbbell. That's pretty much it for the solely lower back stuff. What can I do to get up to 350.
 
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