Idle surge after warm up

[Darrell McAvoy]

I have a 2000 Vortec 7.4L  that idles steady while it is cold . When it gets warmed up it surges from 500 rpm to 900 rpm. I can't find a vacuum leak with carb cleaner but I can hear it hissing when it goes up to 900 rpm.

So far I have put new EGR valve, O2 sensors, idle control sensor and throttle position sensor. The motor has about 4000 miles on a complete rebuild. It's bored 30 thou. and has a RV cam but is stock other than that.Any ideas?