Really need more info to know. LTFT accommodates changes in air density (temp and altitude) as well as fuel variability (and probably other things too). It's expected that it will change in winter compared to summer. You quoted some + and - numbers after resetting. Are these at the same maf voltage? Can you get a log of MAF v., air flow, LTFT and STFT after letting it settle for a 100km or so? Do you have one from summer to compare it to? That will give you a better idea.
You can always check for boost leaks as well.
What fuel are you using? Has it changed? Don't think 'tank' is a good measure for fuel economy - too variable. Try using an app like fuley or calculate it yourself from distance and fuel added at station.
Sent from my Nexus 6 using Tapatalk
Fast: RayD Tune|COBB AP|JBR|Stratified|CP-e|Xforce|Autotech|Denso|Corksport
Turn: Bilstein|Eibach|Whiteline|JBR|Hankook RS3
Stop: Wilwood 4pots|Custom lines|DBA T3|Remsa|TRW 600
Rice: JL|Alpine|Focal|MiniDSP|Rota g-force|2XS|Cree|Celestial Blue FTW!