I agree 100% with skeeterkilr.:thumbsupwell.... i've been told that letting them idle long periods washes the cylinders down. a lot of people have said to keep it under 15 minutes of idle time unless you can get the engine up over 1000 rpm for the idle time.
Efilive can adjust your idle settings, and I believe you can also use the PTO input pin on your PCM to control your idle with a switch.
If you need to idle your truck and need this done, I can help you with it if you would like.
Anyway if you have any questions about it let me know