Overall company wide, Nissan started using them around '82. On the 720 that would be when the Z24 was introduced, Nov of '82 build dates and up. Any build date after July/Aug '82 is an '83 model year truck.
Above about 45-50 the torque converter was locked directly and there was no slip. At that speed it was only a couple of hundred RPM and not really noticeable. There was no 'shift gears' feeling like first to second, it was very subtle. Transmission would run cooler and in theory slightly better mileage. All car makers were getting into this.
Thanx Mike, mine's 3/83 but doesn't have the speedo wires like the 85.
Was there a different lock up switch on the earlys?
The lock up is automatic and governed by vehicle speed. The only electrical on the automatic is the ignition interlock the reverse lights and the kick down solenoid.
The Z24i in the D21 Hardbody has a true 4th gear overdrive automatic with the switch on the floor shift to disable it.