Scotty, addicted to the YouTube. Thanks: Last 2 years as NJ switches over to winter gas my 2011 Rav4 (now with 110k on it) develops a slight idle stumble when braking. Ambient temp doesn't matter.
It has never stalled. Mechanic finds nothing but confirms others have issues with winter gas as well.
Problem completely goes away when the spring gas rolls back out again. Any additives I can look to?
I believe the issue may be due to the RVP or Reid vapor pressure used in the winter vs. summer gas blends.
Winter gas has a much higher RVP that allows the fuel to vaporize at a lower temperature.
Summer gas has a much lower RVP so that the fuel will vaporize at a higher temperature.
Since all gasolines with ethanol are hydroscopic (absorb water from the air), you may also be experiencing some phase separation with the gasoline and ethanol (just a guess).
I have used the product HEET (red bottle - isopropyl alcohol) for decades in the winter time. Follow the instructions and that may help.
I would attribute some of those problems simply to the effects of cold temperature on cars.
Refiners add butane to the gasoline in winter time. I keeps the volatility high so you can start your car easier. But the energy content is lower, so you get slight less fuel economy.
In the summer, they add different additives to keep the vapors and degradation down. Since they are more expensive, this also leads to an increase in prices.
All of these things depend on regional climate and state RVP limits.
Everything is worse in NJ. Try adding some Techron fuel system cleaner to a tank of gas and see if that helps.
"Everything is worse in NJ."
Oh ain't that the truth! 
Have you tried higher octane gas?
Thx everyone. You all confirmed exactly what we thought. Higher octane didn't help and prior to this post I ordered a bottle of the Purple cleaner which also claims ethanol stabilization. Will add that Monday b4 a Turnpike ride and see if there's any difference.
Thx very much Scotty and friends. Doing yeomen's work.
HEET?
ALCOHOL?
doesn;t gas have 10 percent alcohol in it already?
Yes, however E10 can only absorb a small percentage of additional water before phase separation begins to occur. Adding HEET will mix any extra water and the E10 together again so that it can be burned in your engine. You can search youtube for the videos. I use it as preventative maintenance only.
Cleaner didn't change things and neither did HEET. Will have to take up Scotty's idea and bank summer gas in a big tank in the backyard 😀!