Limit switch trips on Atwood furnace

The limit switch trips every time I try to run the furnace. That is why I say that the limit switch trips. I am not saying that the limit switch is bad.
I could not get the exact motor, because of age, but the description said it was compatible. I have not totally ruled it out.
Everything appears to be clean as far as debris. There was a dirtdabber nest in the exhaust area, but I cleaned it out. There appears to adequate coming out.

The motor comes on for @15 seconds, the gas usually ignites, runs for a second or two, then the limit switch trips. Sometimes the limit switch will trip before it ignites.

Are you SURE the new blower motor is exactly the same (not a slower speed one)? A tip for working on your furnace..if the propane hose is long enough, get a trailer 4 pin plug/socket and use that for a quick disconnect for the electric (and add extra length to wiring). This let me set the furnace on a couple sawhorses just outside the RV, connect it and run it fully exposed. Easier to troubleshoot/work on it.

YouTube has 'how to' info ,

Flame Sensor testing; how to easily test a RV furnace

What makes you think it is the Limit Switch??
High TemLimit Switch would need more time for overheating

Flame igniting then shutting down is symptom of 'Flame Proving' failure
That happens with in just a 6=8 seconds

Flame generates an AC current that gets rectified into a DC Current that circuit board is looking for...no signal/circuit board shuts down DC to gas valve so raw fuel does not accumulate.

Flame sensing is via Spark Electrode/Ground Rod
Must be CLEAN cause signal is only a few milliamps

I forgot to mention that this started after I replaced the blower motor that was locked up.
All vents and return are clear.
I had thought about replacing the sail switch, but I didn’t just want to start replacing parts and throwing away money.

Return air vent plugged up, or heat ducts plugged up,(dog hair?) or outlet vents closed in some rooms (open them all)

Remove floor and wall registers to vacuum the ducts out, remove return air vent to vacuum behind it.

It might not be the limit switch, but the flame sensor might not be detecting the flame. Check the prongs in the burner for stuff on them.

not enough air flow. Voltage low or sail switch badbad