My 1995 Chevy Caprice (LT-1 engine w/ 167K miles) runs lean and bogs when it's first started.  After running for 3-4 minutes, it clears up and runs great.  I've already replaced the coolant temp sensor, the O2 sensor, and the IAC valve, all with no luck.  

If I shut the car off and let it cool, it does the same thing when restarted.  But if I restart it while it's still warm, it's fine.  I'm running out of sensors to change.  Any suggestions?  

Sounds like the Mass Air Flow sensor is going bad. Had that happen with another GM car, when it was cold it'd run like garbage, once the motor got warmed up, it'd run fine.  

don't forget the air temp sensor