I know you checked the element, but I will almost guarantee that it is shorting out. Here is how you check it:
1. Bump Test (my own name for it ... you like? lol.) Put one lead from your meter on one of the heating element leads and the other other to the housing of the element. Now 'bump' the heater ... give it a good shake or rap with the butt end of a screwdriver. If you see any jumps at all in your meter, it is grounding out when hot.
If the 1st test does not show anything then:
2. Pull the heater and inspect it. When you get the top shell off, I'll bet that you find the plate between the coils has heated up and warped to the point where one of the coils is almost touching it. Usually at the very back of the element. In this condition, when the dryer gets hot, the coil sags slightly and you've got a short. This means the element does not cycle and gets hotter and hotter until the high temp t-stat blows.
See here: http://neighboursapp...-to-ground.html
and here: http://neighboursapp...ng-element.html
Source: Whirlpool Duet GEW9200LW0