89 blazer help

89 k5 5.7 auto got a prob wants to stall and is idling badly now acts like its cutting out as in missfire have replaced fuel pump filter injectors plugs wires cap rotor temp sensor o2 sensor egr clean and vacuum test was good... seems that when outside tempis in the 30s it runs great untill heat build up under hood 50s or warmer runs like crap from the gitgo any help would be greatly apriciated and needed... im not a mechanic but am able to do work myself and have decent knowledge in this area but am stumped with this one also only code it throw is 44 lean

Possible causes. O2 wires touching exhaust, bad ground from ECM to engine block.
faulty MAF or vacuum leaks.
you can unplug the MAF and if the problem goes away replace it.