You Have cleaned the vent and vent terminal. You said that you checked the damper flap for operation, did you do it from inside or outside. If you did it from inside go outside and see if it has a stopped up varmint screen on it.
The correct thermal fuse kit for your dryer is 279816
(309F) you need to replace the High limit t-stat also included in the kit, IT IS BAD it not opening and causing the element to overheat blowing the TCO. To test borrow your honey's electric skillet, set the temp at 250 place the limit switch on the skillet face down check to see if the stat opened adjust the temperature up a little at a time until it opens, is within it's listed rating?
Dryer Thermal Cut - Off Kit, AP3094244