heater trouble

It being a Suburban in a Class C it can only be accessed from inside.

Could be dirty burner/burner chamber
Could be faulty spark electrode (the electrode is used to prove main flame...milivot signal generated by main flame goes back to control board via electrode to prove flame and hold gas valve open)
Could be low gas pressure

Could be low DC voltage.

The 'sail switch' is making up otherwise the spark electrode would not get power to spark nor would gas valve get power to open. Sail Switch has to make up before any of that can occur.
Low DC voltage could cause motor to slow down when spark electrode/gas valve get power causing sail switch to drop out which then would have to make back up sending power to board.....

Most likely problem is that it's a 1996 and is dirty due to having to remove furnace completely in order to clean it out.....which probably has not been done.

Start with the easy basic.....pull furnace and clean up the blower & combustion wheels, clean out the burner assembly, clean the gas orifice (unscrew & clean with alcohol), clean off spark electrode with emery cloth, clean out the combustion chamber & clean the connector contacts on board with pencil eraser.

Probably lots of rust/dirt

When I had this problem the sail switch had to be replaced.

This Link to Service Manuals might be of help.

The furnace has a way to "prove flame" which means that it feels for heat and shuts down if heat not found. It also looks for air flow which typically is what they call a "sail switch."

Sometimes there's outside access to the furnace, other times not. Ours does not have outside access either.

'Nuff for theory. An easy first step would be see what you can do to make sure the two tubes to the outside of the coach are clear of critter nests. We've seen cases where there was a nest IN the squirrel cage blower inside the furnace. That's going to reduce air flow and shut it down on sail switch.