Need help with strange sub idle issue

[fr8tdog]

In general, if I blip the throttle to lets say 3000 rpm and let off the gas in neutral, or clutch pedal depressed the rpms drop to 490-500 and then recovers back to about 800-900. It seems like this happens more when the car is hot. The car runs very strong and doesn't act strange in any way except for this sub idle issue. I would say that idle seems a bit rougher than I remember, but that could be in my mind. I noticed this issue even before having my ESS tune updated to a new version. I don't remember having this problem until a couple months ago. I did replace my fuel pump and filter because a lean condition that developed. The problem is less noticeable when I have a load on the engine...like the A/C. In summary, I noticed this problem before my catless headers, before my tune revision, before my fuel pump and filter change. I hope I didn't damage something with my lean condition. I also notice a more prominent ticking sound under the hood. I was thinking maybe a vac leak I will try and get it to the shop on Monday and see if we can get it resolved. In the mean time I would like some input from anyone who might have an idea. Thanks guys
Joe