Atwood Furnace Problem

[4000foot]

Hi,
My 2004 Dutchman motorhome Atwood furnace model 8500-IV, 8531 starts then runs normally for 3 to 4 minutes then the burner shuts down and the fan continues to run. The burner restarts after about a minute and the same events continue. Diagnostic LED on the circuit board flashes once every 3 seconds, and according to my manual it is a Limit Switch/Airflow Problem. Replaced the limit switch and found/corrected a crushed hose but the problem continues. Inspected the heat exchanger while I had the furnace removed, and don't suspect the Sail Switch as the furnace starts normally. Anyone ever experience before and corrected it? I'm out of solutions and reaching out. Thanks in advance kids.