Idle in park varies

Is this a normal occurrence? When in park i'm idling around 600, then it jumps up to 1k for approx 7 secs. then come back down. It continues to cycle through that. Some times when I'm actually driving I feel like that is happening as well, I attributed it to "hunting" for the right gear but the truck is at 6600~ miles and i've already had the ATF filled up. As a note I also had my Crank Position Sensor replaced because it caused my truck to stall out on me twice. Any thoughts?

v6 4x4 OR with tow package

 

A/C on?

 

Yes. But i've never noticed it before and it and seems like it appeared after that CPS replacement. Or i'm just paranoid and over sensitive to all the noises that the truck makes.

 

Paranoid. When the compressor kicks on the motor jumps up a few hundred RPM. Turn off the A/C and watch it won't happen.

 

Nice! I'll try that and report back. Thanks!