1998 blazer no power
 

when i first start it it will idle fine and when driving it will pull hills with little problem but once it heats up it barely crawls up a hill. when in park you can slowly get the rpms up but if you punch it - it boggs down. autozone checked the codes and it said mass air sensor and egr i changed the mass air and it didnt help and i was told it couldnt be the egr or it would idle ruff. also changed the air filter and fuel filter and the fuel pumpp is less then 6 mos old...?