Found myself in traffic today, nothing major, rolling along at 20mph or whatever. I locked it into 3rd (IOW, wouldn't allow it to shift above 3rd), which won't allow lockup in my truck. As a result, engine would drop to 1,000rpm while coasting and 1,500rpm at the slightest throttle.
Annoying.
Any other transmission would have done what I wanted to do, to modulate speed by modulating throttle; but this up/down engine rpm was grating.