Well, first of all, which RB are you using (is it any RB for you)? That would help, as some RBs should be able to run for 150 yards, but of course not game to game.. then that would be, or is a problem that needs to be addressed with the sliders, if they actually can be.
One thing I noticed, if you play on slow speed, the running game is just easier overall. It's easier to set up your blocks and get out wide at that pace. Now, I've also seen that contradicted with comments from people saying they can't even get back to the line with their RB on slow, but I've watch enough streams (pre-tuner and post tuner updates) using Armor's base sliders, and I've seen an easy running game for some of the non-elite RBs going off-tackle or wide in general. Easier running going up the middle as well as finding, then seeing and attacking the holes that open up, before they close, all take pace at a slower speed on slow, rather than normal.
Besides that suggestion, how often are you running for 150 yards or more? Is it commonplace? What about against a stout defense? And again, like I previously asked, it also depends greatly on who the RB is.
As for adjusting sliders, I can't think of anything besides adjust the run block slider for the user. This year isn't like M25 where sliders affected other sliders and the penalty sliders also affected the O-line blocking as such. At least after all the testing thus far, it seems like that is the case this year.
I have read from others though (main board, ugh!) that the running game seems easier after the tuner updates, so maybe even if you are gashing the CPU with user run blocking at 0, means it can't be remedied if they did do something to make running the ball easier.
I mean, I use Zac Stacy of the Rams, and he's not that fast, but can truck well. I don't really gash the defenses with him, and my YPC aren't out of the norm for a RB like him. In that Vikings game I called a fair game and called running plays which I felt were on the proper downs and distances, and got around 136 yards rushing against a D that isn't that superb (I don't remember his YPC, they weren't too high).
EDIT: The only other slider I can think of that could do something for you, is if you are breaking too many tackles for extra yardage, up the CPU tackling slider some.