When you say reset, was this a full factory reset? If so, and it's not cured, I'd try again, but leave all you apos off it and see how it behaves. If it's stable, put the apps back one at a time until the problem recurs and that'll be the culprit.
Also, what's the state of your battery? Is it discharging too quickly. This could indicate a rogue process - either core or app, or a faulty/exhausted battery. The process above should sort the former. The latter requires a replacement, which you should be able to get by mail order if nothing else.
If none of that works, a repair may be necessary and you should be able to fund a local one via the Samsung website.
