FAST START IDLE

Just bought a 1996 chevrolet suburban k2500 with vortec 7.4 v8, I have check and there are no codes in the system, diagnostics have required that both o2 sensors(up stream), icm, and map sensor be replaced. My problem is that every time the vehicle is started the start idle starts at 1800-2000rpm. Most the time is will settle to 600-800 rpm but sometimes it will sit at 1000rpm til it is driven a short distance.I have checked for vacuum leaks, replaced the iac and have also replace the egr gasket when removed and cleaned. The vehicle runs great except for the starting high idle.