My 2000 Chevy blazer 4x4 V6 revs at about 2500RPM when I start it and then SLOWLY drops to around 1500RPM which is still not normal(should be 1000RPM in Park/Nuetral and around 600-800RPM in Reverse/Drive). When I put it in Drive it goes all the way back up to 2500RPM and when I come to a stop it wants to stay at the same RPM until I am stopped and then SLOWLY goes down to about 1500RPM. I have replaced the Throttle Possition Sensor; Idle Control Valve and PCV valve. I have cleaned the entire Throttle Body and cleared it of all Carbon that could cause a sticky throttle. I'm at a loss as to what it could be. Since a shop will charge me an arm and a leg I would like to fix it myself. Any ideas?