So the torque converter is pretty simplistic at the moment, and it'd be nice to have it like this: table starting at 1st gear, so 1500RPM=1st gear low lockup lowLockUp:[1500,1300,1000,800] (values for a bus so RPM is low) highLockUp:[2000,1700,1600,1600] (again for bus). This way on vehicles with a low amount of gears, eg.4 they can slip in and out of the torque converter locking phase quite easily, this is quite normal for cars, as the torque converter can unlock to squeeze out some extra power.
