A model number may help others help you.

I am assuming that the thermal fuse you are referring to is the one on the blower assembly.

The most common cause of this blowing is the vent system not the lint trap.
Check/clean your vents system.
Also make sure that the exterior vent louvers are open properly.

Check/clean the blower wheel.

Check your heating coil.
If this is the problem you probably cannot get lower temperature on low temp cycles.
Also it usually blows the thermal cut-off on the heater.
Unplug the unit and both wires to the coil.
Check it with a meter, should be around 10 to 12 ohms.
Then check from each side of the coil to the case/frame, both should be infinite ohms (open). If not the coil may have sagged or broken and is touching the case. This can cause it to run on high and the thermostats cannot regulate it.

If everything looks OK I would replace the cycling thermostat, could be it is sticking closed every once in a while.
It also is on the blower, I think.