if you are batch sparging runoff speed has nothing to do with efficiency. Also, fly sparging does not necessarily result in higher efficiency.
I'm guessing you don't actually mean .35 on an inch as that's pretty wide and I would think the grain would just fall through. but .035 would be fine. Maybe too fine, but if you are not getting stuck runoff then it's not too fine!
The next thing to look at is your measurements. It's not possible to calculate efficiency accurately without accurate measurements of all volumes, weights, and gravities.
If those are all right on then water chemistry is next on the list.
+1 For all of these! Need grain weight, strike water volume, sparge volumes. Also, where in your wort flow are your PID temp sensors? Are you stirring your mash after you add your sparge water infusions? How fast are you recirculating? You may be getting some channeling during your conversion time, then when you sparge, its not circulating through ALL your mash bed.