Hey ND!
You must be talking about last year... . there has been no winter yet this year.
I have tried 15W40 semi synthetic (Premium Blue 2000), 15W40 full synthetic (Amsoil) and now 5W30 full synthetic (Amsoil). There is no comparison to the 5W oil. Even the full synthetic 15W40 still crank hard and had slow oil presure.
Thin oil does not equate to synthetic. 5W oil versus 15W40 is what it takes up hear.
Find some Mobil 5W40 or Amsoil 5W30 (Series 3K only). Run it 2X as long as you have been changine your regular oil. Change filter at normal change (3K, 4K or 5K). It is worth the money and it does make a big difference.
jjw
ND