Help...cant figure out what's wrong
 

I have on 08 LTZ with the 5.3L Flex fuel. We have been trying for months now to figure out why it keeps throwing codes p1174 and p1175. Here is a list of everything done, my mechanic is cursing this thing....just wondered if anyone here had any ideas.
All 02 sensors & spark plugs
Fuel pump assembly
All 8 injectors
Mass air flow sensor
Oil pressure sensor
Checked for intake and exhaust leaks and fixed
Called gm to see if there was any updates for the computer
Checked to see if fuel pumped is putting out what it should it is.
I have a chip that is a code reader, which says I have a lean condition in bank 1 and 2
Should also mention there is an extended crank to start sometimes, but only after you drive somewhere and it sits for a bit, then you come back out to start it. If you step on the gas it fires right away which makes no sense with fuel injection. First start in the morning is always fine, fires right away. Since most of these repairs were done, there is no longer an issue with it being sluggish, and is shifting the way it should, before it felt like a boat anchor and I really had to mash on the gas pedal to get some giddy up and go.