If your winning heat races against same competition at 5 & 4 lb of air that tells me your close maybe could go 4.5 & 5.5, NO low to medium bite track changes that much from heat to features to warrant 8 lb Lt and 10 lb right your taking to big of a swing at it killing your forward drive, and don't do a 2 lb split only do 1 lb split try 7 lb & 6 lb.
Confirmation your on a flat kart ? Not champ ?, are you running same set of tires for your features ? If so are you wiping less ? What are your cambers set at ?
Then sometimes when it was dryslick in the heat it was so loose ass end with 9 and 6 with that air pressure I was just experimenting with!