My Kenmore Elite, heavy duty, electric dryer stops mid cycle. There is heat but it doesn't finish the cycle so clothes are dry. Strangely, I tried flipping the breaker on-of-on (which was NOT tripped) and it started and finished the cycle. Now that doesn't seem to work. I've tried both cycles (times and auto) and it happens every time. Any ideas?

Bad timer? Or maybe dryer getting too hot causing auto shut off.

The dryer getting too hot is something that we have recently experienced on an old Hotpoint dryer. It has a bad auto thermostat in the return, so if it gets too hot on the auto dry cycle - it stops and will not re-start until it cools down.
Your situation could be similar, and/or it could be caused by either lint or something else clogging the vent - thus causing it to overheat. You should be able to feel the top of the dryer right at the back of the top - near the console right after it shuts off. If it is getting too hot to the touch look to the items I have mentioned.
If it is getting too hot, this can be dangerous - so be very careful, and don't run it with no one close by. Know where the breaker is - just in case.

Knuckelbuster is on the right track with the overheating. Usually when a motor overheats it will shut off by a heat sensor built into the motor. One way for you to see if that's your problem is after it shuts off, walk away for an hour to let the motor cool down and then restart it. If it starts, runs for a while and then does the same thing then very likely it's the motor.
Several reasons a motor overheats is that it's loaded with lint, that it's not getting enough voltage or that the load is too much because of bad bearings either in the motor or in the dryer. If it's the lint problem it needs to be blown out with air. Low voltage could be a couple of reasons, one being on a long extension cord or bad house wiring in older homes.
If the dryer is old or you do an awful lot of laundry, it may be getting worn out.
An AMP meter would come in real handy in order to find the low-voltage problem.