If Earl is correct in the track being hard, then it sounds like you were too soft on duro, and if that's the case, it should show up with excessive tire wear (feathering on the inside shoulders.)
Now, if the track simply sealed over and turned black (but still did not bite up = fairly common on some of our northern states tracks,) then it could be that you simply didn't have enough bite in the tires.
If the track uses soap powder, that tends to seal the track up and yield little to now bite as well.
On a hard, dry, track - you increase your tire pressure if you are seeing pressure gains, need more roll speed, track bites, up, etc. Not all hard dry tracks bite up though.
We need some more info.
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Thanks and God bless,
Brian Carlson
Carlson Racing Engines
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