Me too. Compared to Alaska's winter blend, the winter fuel here in Wyoming is complete garbage. You'd think these northern states would have it figured out....
The LBZs and up I would guess where changed to place a little bit of a load on the engine to aid in the trans warm up.
I've never had my truck not shift into 5th/6th if it wasn't warm. I also have a remote start and don't live in a cold climate, so I never really takeoff in a cold truck.
A 2mpg drop in MPG in the minimum you can expect from what I have seen when going to winter fuel. When I head north its like someone flips a switch and my MPG drops.
My LBZ locks at 73* and my LB7 locks at 84* but iirc there is a table in the tcm on my 01 that i changed because it would never lock up if the temps dropped down to 20 or lower.