Idle Question

[allterrain08]

I've had my 08 Sierra (5.3L) for about a month now and when I am stopped at a light or whatever the idle drops to about 500 RPM and when I put it in neutral or park it jumps back to about 6 or 700 RPM. I think 6 or 700 is to low when it is jumping back and forth and I know 500 is to low. I am just wondering if I should bring it back to the dealer and get it checked to be safe or is this all normal? (It's my first truck, first automatic,etc...)

[Fortune50]

I haven't noticed the rpms at idle on my '01 6.0, but on my '01 Z28's 5.7 LS1 (which I bought new), it would occasionally idle at 500 rpms in gear when the weather was pretty warm out...btw as long as the actual engine rpm is within 50 rpms of the "commanded" rpm, then it's ok. It actually won't set a code until 100 rpms below commanded on ETC (electronic throttle control) systems.