Vacuum leak trouble?

99 pontiac gtp, 130K miles, reprogrammed pcm from digital hp, throttle body spacer & wizaird CAI, 180 thermostat, recently purchased and installed zzp stage 3 intercooler came presealed, zzp fuel rails, zzp ported SC case, zzp ported LIM - rpms at startup shoot to 1500 and slowly climb to 2500 where they don't go any higher. I am throwing an IAC code forgot the specific number will rescan and post later . . .
The IAC was replaced before the massive install, and I even cleaned the throttle out at that point and made sure the pintel was less than 28mm upon install. I have redone the gaskets between the IC twice with rtv (garlock on the bottom, oem on the top, because I destroyed an oem during one removal and didn't have time to go buy a new one), I did place the four corners of rtv on the head gaskets for the LIM. I have placed a smoke machine on the vacuum lines and fixed the few small leaks found on some of the rubber connectors on the vacuum lines and LIM to EGR pipe. No fuel leaking by the injectors or along the lines. I even went back and placed rtv on the throttle body spacer gaskets - just in case! Also tried spraying carb cleaner on select spots with the engine running and haven't discovered any changes in idle. . .
That all being said, any ideas on what to look at or try next?

LIM gasket vacuum leak into the crankcase?

It would help to post the IAC DTC. Did you run an engine vacuum test?

The Garlock gasket is probably part of your problem.

Good looking out tblake and bnaylor for the quick responses to the post . . . here is the followup info:

P0507 - Idle Air Control System, RPM higher than expected is the SES code I'm getting.
Also with the vacuum test I'm getting 17 inHg on startup idle with about 1500 rpm and as it climbs to 2000-2500 rpms the gauge read about 18-19 inHg.

Btw, I noticed after the vacuum test a very light hissing sound like air being relieved after the engine was shut off before the gauge disconnect . . .I was standing on the drivers side of the car when I heard it but didn't see anything visual as to what/where the noise could be coming from!?

Am I still looking at a vacuum leak, sensor problem or am I completely off key?

Engine vacuum looks good. I'd concentrate on the IAC DTC since that is the only concrete abnormal indication you have. For the P0507 DTC you can check the PCM 5 volt reference signal to the IAC. The DTC indicates high resistance in the IAC circuit causing high IAC counts. Other causes could be a skewed throttle position sensor (TPS), MAF sensor, PCV valve, throttle body - (stop screw, linkage or throttle plate end seals, carboned up) or any intake system vacuum leak.

Problem Solved: Throttle cable end screw was adjusted too high on the cable, released the excess cable, no more high throttle! Sometimes its the simplest solution . . . thanks bnaylor! Luckily I was also able to diagnose and fix a faulty MAP sensor in trying to remedy this issue. Hopefully this thread helps others solve similar woes associated with that dreadful code, as I have reviewed many posts on many different forums without any solutions actually posted.