FDKAPLAN

Hi, I have a 2014 Forester (approx 36K mikes) with a recently replaced short block. The idle as times (before the short block replacement) was less smooth (especially in colder weather) that at times I would put into Neutral just so it would idle smoother. I was told that the not smooth idle was due to the CVT. Now since the short block replacement, it seems to my ears that as the gas tank gets lower than a half a tank, the idle is too low and not smooth. Again, at times I find myself putting the CVT into Neutral to smooth it out. Any thoughts, suggestions as to what this could be? I mentioned it to the Dealer the last time the car was in for service, but any updating of software, etc. hasn't improved the situation. Thanks! Fred Kaplan