Very poor mileage on m 2004 Pathfinder Chinook 3.5L

[Blakbrd]

Hi Folks,
Just joined the forum and my first post. I haven't looked through entire list of topics and suspect this has been asked before. Up until recently I would get between 125-150 kilometers on first quarter tank of gas and recently that's dropped under 100 sometimes down to around 75-80. I am in western Canada and it is winter but this is first year with such poor mileage. I have 205k kilometers, one owner and have taken care of my vehicle these past 10 years. Very little other than normal service has been done. My air filter is quite new and no unusual sounds other than occasional squeeling of some belt when in wet weather. I have had belt replaced during lifetime of vehicle. I use premium and mid grade gas. Another question is when weather is extremely cold (-25 or less) my tranny is in auto but the little yellow light in centre comes on for awhile and then goes off after driving half an hour or so. Does the tranny automatically go into low because of temp?