I never thought about the tackling slider acting as though it was a run awareness. Not sure if its true or not but looking at your sliders I'm guessing its tougher to run since you boost the CPU run defense over default (human run block 40 vs. cpu break block of 50). Furthermore you reduce the running back ability to 35 making them less effective and boosting the CPU tackling to 75 for a 40 point advantage there. I'm guessing you also rarely break tackles because of that. I think your run sliders are probably tougher than what most play on which is why they find it easier.