Yes the TPS can be a cause of the, torque converter unlocking and locking up again. The vibration of the throttle shaft, causes the TPS wiper to etch the carbon tract, to form a bad spot. This usually is at the throttle position that, the car usually cruises at.
The Overdrive term is just that, to drive over the 1:1 ratio.
As Dave says the gearbox gearing is higher/over 1:1, so our 4th is an overdrive ratio, as 3rd gear is 1:1.
This really does not mean as much to-day as it did when we had 3 speeds and a add on box, to provide an OD ratio. Now most boxes have 4th gear at an overdrive ratio.
Locking the converter, is more about economy than raising the ratio, as it can lock in other gears too.
Harvey.