What were the year to year standard feature changes in Gen 2 2500 diesel?
If I've heard right you could read codes on the odometer by flipping the key on and off three times starting in 2000. Anything else?

 

This covers the engine aspect of the evolution:

http://dodgeram.org/tech/dsl/Facts/epa_changes.htm

As far as the truck itself , i am not sure of any timelines.

Your truck has the ability to display codes in the odometer window , cycle you key on-off-on-off-on , and leave it there to display the codes.

 

You can do the same thing with most any car. You get yourself a Haynes repair manual and that will tell you how many times to cycle your key on and off. Then you count the number of times the check engine blinks and you get your codes that way. That’s how I use mine to trouble shoot when the truck is acting strange.