I am on LP and have no build up on my pans. I assume carbon build up would be black soot?

The culprit is not LPG but it's bad combustion due to altitude (air contains less oxygen, flame is orange rather than blue).

I have two cooktops in two different kitchens in a mountain house. One had your same issue, the other didn't, although both of them are fired with the same LPG.
Once the small nozzles/orifices that are used to mix air and gas have been upgraded, the issue disappeared and the flame turned blue

Thank you eandhl and hidroman. I assumed it was a flame adjustment problem and not the LP that was the culprit. I feel better now, thanks!