Greetings! Have a 1999 Sierra Z71 with 5.3L engine, last winter service engine light would come on when engine was started when very cold only. Check of codes showed P0171 and P0174 fuel system lean bank 1 & 2, after posting determined fuel pump pressure low, replace MAF, EGR valve, fuel pump, fuel filter, & fuel pressure regulator over course of several weeks attempting to fix . This improved problem but didn't completely go away. By time all of this had been done it warmed back up and no problems since. Since it has turned cold again recently, had service engine light come on when engine was cold and sometimes after this happens it will idle fine but surges in 15-40 mph range. At highway speeds it runs fine. Rechecked codes and found P0405 EGR sensor A circuit low. Truck has factory engine heater and when it is plugged in overnight problem doesn't occur, but when parked at work for entire day and then started cold it will trip. Suggestions on possible places to look to solve problem? Any help would be appreciated! Thanks!