Gas Recirculation Valve (egr Valve) problems of the 2013 Subaru Legacy

The car intermittently loses power when accelerating from a stopped position. Most often happens when I am turning left. Subaru says there are no computer codes in the check engine history. Cause unknown but speculation advanced about neural network learning of the computer (seems worst after recent engine rebuild until car was driven for a couple of days where frequency of power loss diminished but not go away). Also proposed: 87 octane gas-should use 92, if not 97 only from oil company stations, not fred meyer or costco even though car is rated to accept 87 octane gas. Other hypotheses: full gas tank vs 1/2 or less , fuel starvation causes power drop (note: engine doesn't fully die & can be coaxed back to life by pumping the accelerator), electronic ignition system perhaps the culprit. This problem is dangerous because of the random & sudden (without warning) loss of power which any driver immediately behind my car would not be expecting & thereby cause a rear-end collision. Also, dangerous when entering a lane of traffic & suddenly the power is gone just when you need acceleration in order to merge at traffic speed into your lane. Sometimes problem occurs when going up a low angle incline (est. 10-15 degrees?) but not necessarily. When leaving a stopped position, if left foot is on the brake & right is slightly accelerating in order to pull away more rapidly from stopped position, the controlling computer will sometimes provide zero power to the accelerator but this happens only occasionally & often will work just fine to give the extra acceleration needed. Subaru says this confuses their computer & it will shut down but I have found that this happens about 1/3 of the time, in my experience. Danger comes from losing power during the time you need it the most esp. Left turns which cross traffic lanes before you can merge and driving completely normally.