It could be a bad O2 sensor. They dont always trigger the CEL when they go bad. Either check for codes diagnostics or physically test the sensor as shown here... O2 sensor
There is also a general drop of mpg's in the winter due to oxygenated gas but not to the extent of 14mpg. Fresh plugs/wires/cap/rotor and timing might also help.
P.S. Hello from up the river and welcome to the forum. <img src="/forums/images/graemlins/cheers.gif" alt="" /> I actually live north of Hudson. Send me a pm if ya like.

'04 Taco x-cab 3RZ FE stock (daily driver)
'90 x-cab 22RE stock
'82 Hilux 6" lift (ACES HI)
'82 2-Hiluxs' Rally Edition (parts)
'81 Hilux 3" lift (parts/restore)