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The reason your fan comes on before your furnace ignites is the "sail switch". It has to sense air flow and close a micro switch before it will let gas flow.
It is possible that there have been a bad batch of switches installed or that they are set incorrectly. That could be the same for the "high temp cutout" switch. Either switch being faulty could cause this problem.
I think the easiest thing to check would be the air flow coming into the thermostat from the wiring channel. That would be a quick check.
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