FWIW: I’ve found the most important factor in moving a big heavy car is effectively utilizing your “torque peak”. For instance, my car FEELS like it’s pulling through 6700. But when I short shift it at 6200, car goes faster. It isn’t always whether or not it’s pulling at the upper RPM, it’s balancing that pull against the torque you’re shifting back into. In order to use your torque effectively, you want to land right on your torque peak with your shift, if you land beyond it, you may be losing ET by letting the engine wind too long even though it still is making power at that upper RPM.