You will need to monitor the voltage to determine whats going on when it shuts off. First, monitor voltage at thermal fuse to ground. Should be 120vac with dryer running. When it shuts off, if voltage drops significantly then could be faulty timer. Monitor voltage at timer BK terminal. If voltage remains steady there but drops at thermal fuse, then timer is bad. You have the wiring diagram, if you get the gist of what I'm saying, then it should be no problem figuring it out. If your not losing voltage at thermal fuse, then you need to check out the neutral circuit which includes door switch and motor switch. Check connections at motor connector. Check for lint buildup inside motor. Could be overheating and tripping motor thermal overload. May also be failing connection at power cord terminal block.

Eric