[American Viking]

Well most modern automatics lock up the converter as quickly as they can.
Otherwise input power from the engine is wasted as slippage in the converter.
High end obdII diagnostic tools and reflash programming tools can tell you what the lock-up point in the transmission is or what the parameters for lock-up to be called for.
Modern transmissions don't have a single lock-up point, instead they have a table based on gear, throttle position, load, % slippage and even transmission fluid temperature.
The best way to sense if the converter is locked or not is to goose the throttle while watching the tachometer. If the rev's rise without the car reacting with increased speed, then the converter is not locked.

It used to be possible to just rig a switch in parallel with the factory electrical signal to trigger converter lock-up at any speed. I know for dirt track cars, we used to use the shift light trigger on an aftermarket tachometer to lock up the converter.
I guess you could use an arduino to do that now.