I don't have a best t3 but i'll try to help you with explanation as far as possible from my side
For the first turn in sector 3- you need to stay close to the walls on the right and brake a bit earlier to get early turn in and drop to third gear and stay a bit tight for a good exit you need to be close to the entry of tunnel , and hammer the throttle once you get in the middle of tunnel by the time you reach next corner stay in middle of track and in 3rd gear drop the speed to 105km/hr on the apex just before the monkey turn which is a left handed turn. Then again hammer the throttle once past the apex ,there might be a bit understeer and watch out for the wall on right
The next left hander stay on the right as wide as possible stay in 3rd drop the speed to 85-90km/he once through the apex hammer on the throttle again but you can get caught by the understeer and also get sunked up in the grass and bounce just before t3 split