Even with the custom tune I had done on mine, the best change was to delay the TCC from engaging which eliminated what your referring to as lugging in overdrive.
It's a 4 speed with a Torque Converter Clutch (TCC), that when engaged, makes it feel like it's shifting into overdrive and it will "lug" under low to moderate throttle positions. It then requires you to stomp on the gas pedal to disengage the TCC or you can tap the brake pedal and do the same thing to accelerate.
But I definitely preferred the late engagement of the TCC so it doesn't lug.
That alone is worth modifying the PCM.