I don't think Jr showed his colors in practice. And you won't see it all during the race either until about 20 laps to go if he'* in the top 5, 50 laps to go if he'* running in the top 10.
He has a reputation (like Mark Martin) for 'lurking' and saving his car for the finish, while never letting the competition REALLY know what he'* got. Early in the race, he'll test all the grooves, then move to his favored groove late in the race, or switch to a different groove for a pass if needed. He'* sneaky.
Genetics and several beatings made him a good driver.