Since it has turned cooler I have to drive for 3-5 miles before my transmission temperature is warm enough for the converter to lock. My engine temperature will have been at normal operating temperature for quite some time before it locks. Why did Nissan program the computer to require the transmission to be this warm before it locks? Is this normal?

 

yes...

 

How do you know when it locks up?

Is it something you feel or how does that work?

 

When you give your engine light throttle in OD above about 38 mph it should be locked. The rpm will go up only as the speed of the car increases if it is locked. If it is unlocked it will show slippage and the rpm will rise quickly. When your converter locks it feels almost like it is shifting into a higher gear when accelerating.