. The issues was the "Sail Switch" inside the fan housing that verifies air is flowing before turning on the flame. My sail switch was either gunked up or reseating the connector resolved the issue. Had to pull off the cover and exhaust port from the outside of the RV in order to access the blower.
Shout-out to Troy Gurley whose YouTube video: 'Suburban SF30 Sail Switch Problem'
provided the solution.
Thanks @twinboat and @topdownman for your suggestions. Always start with the basics!
P.S. I also spoke with Tiffin customer service who suggested that the furnace 'overlimit switch' may have gone bad. That appeared much more difficult to access and would have required pulling the furnace out of the RV as far as I can tell, so I'm extra glad I found Troy's video before attempting that.