Erratic idle in gear?

[1BAD68]

When my Charger is in neutral it idles at a steady rock solid 900 rpms but when put in gear the idle drops to 850 and fluctuates about 50-75 rpm up and down.
Is this a sign of vacuum leak? Any ideas?

[68X426]

Doesn't seem out of the ordinary to me. 
My Hemi does pretty much the same (more like 25 to 50 rpm). 

[471_Magnum]

Make sure you aren't pulling any vacuum on your timed port causing your timing to jump.

If you have vacuum at idle, that means you've got the throttle open too much, probably due to a lean air fuel mixture at idle. Could be lean due to a vacuum leak, or just out if adjustment.