Engine Revs To 4,000 When Strated

[Kyle2505]

I posted this on a different part, but i think it better suits this section. I have a 99 GMC sierra 1500 5.3. I recently had very bad sludge in the oil and an internal coolant leak so i replaced the head gaskets. When i got it all put back together, i started it and it reved to about 4,000 and stayed there. the throtle doesnt open when it does this so i thought it sounded like a very bad vacuum leak to me so i checked the brake booster hose and the PVC hose for leaks. Nothing. It sounds like its going from the air fliter box. could a bad IAC valve cause it to rev this high, or maybe a bad computer cause it to open the IAC? Besides the booster hose, pvc hose or cracked intake manifold, where could a vacuum leak come from? Any thoughts or suggestions are greatly appreciated. thanks