I'm almost Positive it's your IGNITION SWITCH!
The contacts have become Dirty, and is not allow a full contact.
I had this same problem, and the same symptoms your describing. I did the Fix following Bill Curlee's Advice, and everything has been good for some time now. The Fix looks more Complicated than it is. Took me about 2 hours.
Here is the Fix
Oh you should swap out the battery as this may be your problem. Around $85 for the AC Delco Pro 78-6YR/7YR Series has like a 7yr warranty with a 30/50 month free replacement. For about $100, you can easily isolate that item. And if you had to jump it already the colder air of winter puts stress on them, the weaker one's fall out quickly. (Battery must have a 120 reserve capacity rating.)