Ford Repair: Code on F-150, vacuum leaks, o2 sensors

Question
I have two OBD codes on my 1996 F-150 5.0L V-8.
Code 171 and 174 tells me of a lean mix on bank 1 and 2.   What could cause these codes and in what order should I focus on repairs or replacement parts?

Thanks in advance!  

Answer
Hello and thanks for the question...I'll try to help.
Check the following:
1. Over all tune up conditions of the engine.
2. Fuel pressure
3. Check for vacuum leaks.
4. O2 sensors..... bank 1
5. Reset fault codes after check and repair and rescan.
Erik