Is this strange behavior for a red eared slider?

RES 5.5" , water temp 76 degrees Fahrenheit, will edit with basking area temperature.

1. My red eared slider very very rarely basks. Maybe once every two weeks it will go up into its basking area a couple of times that day for about 30 minutes maximum.
2. It will sit at the bottom of the tank standing on one or both back legs, standing perfectly still and sometimes sleeping. It always did this occasionally but started doing it more recently. Could that just be because it's winter? Tank temperature is at 76 degrees Fahrenheit. It does this for a large amount of the day, but if you go near it then it will quickly get up and start swimming toward you. This area is not where it sleeps at night, at night it will sleep in the area under the basking area (the turtle topper has a platform underneath of it) I dont think he's vit-d deficient since the light that lights the water is UVA/UVB.

I'm also not sure if it is a male or female. it's claws seem medium sized so I havent been able to figure it out. I can upload a picture of the bottom of it's tail if necessary.