[deeesstoronto]

The high temperature limit switch should never be tripping, even when the furnace runs continuously.

This indicates you have a problem with temperature rise across the heat exchanger, probably from inadequate airflow. Your ducts may be sized too small/furnace too large, fan speed set too low, plugged filter, etc. You may be able to mitigate the problem by increasing fan speed, limiting heat by using stage 1 only, putting in less restrictive filter, add additional cold air return, etc.

Usually a failed limit switch means cycling and a bigger problem with airflow. However I have seen a high temperature limit switch fail without cycling - fell apart with age (40 year old furnace).