new strange gas gauge behavior

I filled up a few days ago. I was down to 3 bars. I squeezed 5.2 gallons into the tank. THE GAS GAUGE NEVER SHOWED FULL. It was 1 bar short. I figured ok, it's just one of those things. It was very cold out at fillup (7 degrees).

So I filled up again today at 2 bars. I really squeezed the juice in to make sure I got a full tank. Temp was about 20 degrees. Same thing. 1 bar short of full. So I drove the remaining 45 miles to work, and what happens? The gauge moves up to full AFTER 40 MILES. ????? Driving home, it lost the 1st bar after about 20 miles.

Anybody else notice anything like this? Is it the cold preventing the bladder from fully expanding? I have never seen this before, but I got Sparky in March and this is the coldest weather she's seen. No, I have not had the gas gauge/filler pipe TSB done, although I have received a notice that I'm included.