Here are your parts
Model LTE6234AW1

Here is the tech sheet
https://www.servicematters.com/d...0Sheet%20-%203398986.pdf

You will see that they show the High Limit and a Thermal Cutoff as a set.
This usually indicates that it is a good idea to replace both.

The high limit should not come into play if everything is working OK.
It is a safety device
The unit should run on the cycling thermostat.

Does sound like an air flow problem, could be
1. Coated lint filter. If you use fabric softener it can coat the filter screen greatly reducing air flow. Clean it with soap and water.
2. The blower wheel may be stripped so that it is slipping on the motor shaft
3. The blower wheel is clogged up with lint
4. One of the seals on the blower to lint filter is shot
5. Drum seals shot

You are sucking the air through the dryer and then pushing it out the vent so anything that allows air leaks will reduce the air flowing through the heater assembly. This will reduce the temp in the drum causing longer dry times. Also may explain why the thermal fuse on the heater assy blew.

They are not difficult to change Take the old ones off, clean up the surface, glue on the new ones, let the glue set and reinstall. You have to pull the drum out to do it so unless you know they are shot I would not.

Sort of stumped here, my gut still says it is an air flow problem but everything looks OK.

Only other thing I an think of is that the cycling thermostat has gone crazy and is not opening/closing consistently at the set points. The norm for these is to fail by either welding the contacts closed or blowing the contacts but it might be the cause.

Unit was running cool, you replaced the high limit thermostat which should have no effect at all. then the thermal fuse blows. Something has changed!!!

Remove the wires from the heating element and check them to the case.
Should be an open. This will check for a grounded element. This is a long shot.

Hopefully others will jump in with more possible causes.