It sluggish after a few laps. Does it blow a bit smoke at corners? When the engine is at optimum temp and less fuel, it gradually be come lean. You can richen the LSN. On test bench, tank just a little less half full, engine at temp, from half throttle to idle, how long does it drop to idle speed? longer then 5 seconds, LSN maybe too lean. Try that! HSN is always constant, LSN mostly adjust during races on pitstops. Another way if your RX has speed control adjustment you may slow the servo. Depends on driving style. Good Luck!!