To put it as simply as possible:
Stock ZJ converters are 1800 rpm stall speed for 4.0 and 5.2, 5.9 converter is 2300 stall.
Stall RPM is the maximum RPM the converter input can turn with the output at 0 rpm. This is also the point where it will deliver max torque multiplication. Under lighter loads (less throttle), the RPM won't climb as high on takeoff, so it's not like it'll climb to 2500 and then go or anything. It doesn't, however, lock at the stall RPM (although it feels like it). Under WOT (especially at lower vehicle speeds) there's a good bit of slippage / multiplication going on.
The lockup clutch is controlled by the computer and is applied to completely lock the converter input and output together when driving at a high enough speed. This reduces heat production greatly. It has nothing at all to do with RPM, other than the minimum RPM for the computer to command lockup (which is about 1100-1200 in 4th on a stock 5.9). It's possible to add a switch to manually engage the lockup clutch on the RH box.
So if you were to hold the breaks on and rev the motor in drive, as the wheels start to want to turn thats the stall speed, look at the rev counter. Thats the point where its like dumping the clutch on a manual. Obviously on the road with normal driving you dont get the mechanical resistance as you would with the brakes on so it will move but will slip. As the appropriate speed point is reached it really starts to hussle as the convertor isnt slipping anymore ( its locked up). If it were locked up all the time whenever you came to a halt the car would stall like a manual stopped in gear.
With a bigger cam you need to get "on cam" as soon as possible so one would get a higher stall convertor, change the gearing or both depending on application.
