Hopper, I would start with a new operating thermostat, since yours is obviously not keeping the temps within normal limits. Also, replace that flex duct with semi-rigid metal duct available at most HD or Lowes stores. You can't afford to have a double-whammy of a vertical vent plus bad duct on a dryer.
Also, it's a good idea to inspect the heating element to be sure it is not sagging or touching any metal parts of its housing, as this can cause fuse failure. A poorly connected power cord will also blow thermals.
The thermostat for your machine is shown below, and you'll find it mounted on the blower duct.
Bias Thermostat- click