I have two code PO0171 and PO0174 it says my bank 1 and bank 2 are lean is this a problem with my fuel flex?

code p 0171 refers to system too lean bank 1===causes --intake /exhaust leak---AIR system---MAF/VAF sensor---fuel pressure/pump---injector/s---HO2S
In this case I would suspect the heated oxygen sensor (HO2S)
then check fro a cracked flex section in the exhaust before the cat converter
code p 0174 refers to system too lean bank 2---causes intake /exhaust leak--fuel pressure/pump---injector/s---AIR system---hose connection/s

code p 2096 refers to post cat converter fuel trim(FT) bank 1 ---too lean===causes --cat converter---exhaust leak
it also refers to heated oxygen sensor (HO2S) 1 bank 1--range/ performance --circuit high====causes --wiring short to positive ---HO2S
replace the HO2S using the correct socket so the wires do not get damaged
for the first one check for an exhaust leak in the flex section of the exhaust pipe under the steel mesh

P0171 ; Fuel Trim System Lean (Bank 1)
P0174; Fuel Trim too Lean (Bank 2)
fuel trim is system to modify injector pulse if system go lean it will go rich when the system is too much lean and is max.rich it code
look for 02 sensor bank 1 and 2 data
hope it helps

Dear friend,you mean you dont know which code is for your 2006 Chevrolet Silverado 2500HD 2WD ,right ?

I've come across these codes before. In almost every case there was an air leak in the intake air hose (hose between the engine air filter & the throttle body). Inspect this hose & tubes attached to it. This is especially true when the lean code includes the comment 'at idle'
P2187 - System too lean at idle Bank 1
P0174 - System too lean Bank 2
P2189 - System too lean at idle Bank 2
P2195 = HO2S Signal Biased/Stuck Lean (Bank 1 Sensor 1)
P2270 = HO2S Signal Stuck Lean (Bank 1 Sensor 2)
P2272 = HO2S Signal Stuck Lean (Bank 2 Sensor 2)

P2187 & P2189 = In order to provide the best possible combination of drivability, fuel economy and emission control, the PCM uses a closed loop air/fuel metering system. The PCM monitors the HO2S signal voltage and adjusts fuel delivery based in closed loop fuel control. Changes in fuel delivery will be indicated by the long-term and the short-term fuel trim values. The ideal fuel trim value is around 0%. The PCM will add fuel when the HO2S signal is indicating a lean condition. Additional fuel is indicated by fuel trim values that are above 0%. The PCM will reduce fuel when the HO2S signal is indicating a rich condition. Reduction in fuel is indicated by fuel trim values that are below 0%. The DTC relevant to fuel trim will be set when the amount reaches excessive levels because of a lean or rich condition

code P1128 02 sensor bank 1 lean
code P1129 02 sensor bank 1 lean to limit
code P1133 02 sensor bank 2 lean
code P1134 02 sensor bank 2 lean to limit

fuel system is lean.

system too lean in bank 1. clean your mass airflow sensor, replace fuel filter. iff all else fails check you fuel pump.

those codes are for lean engine condition look for vac leaks at the back of engine to the pcv valve could hear hissing noise with engine running also check egr valve to be stuck open also when was last fuel filter changed? hope this helps .

ALL CARS fixes are guessing and hoping at best. 1st thing is it a 4 cylinder or a v6. if its a v6 and you have bank 1 lean but NOT bank 2 lean, then you are probably looking for a vacuum leak affecting only bank 1. Stuck injector will NOT ause this code without also setting a misfire code. Cars use fuel trim. Basically you have BASE FUEL which is the preprogrammed best fuel amount for each condition. FUEL TRIM is the result of when the o2 sensor analyzes how rich or lean the car was, then adjusts the fuel trim to compensate as needed. Most cars set a trouble code around +/-25% fuel trim. You really need look at datastream on a scantool and determine if BANK 2 is also lean and just not quite at code level (IE - Bank 1 is at 25% and set a code, Bank 2 is at 22% and did not). In this case, tream it as a problem that affects ALL CYLINDERS instead of a bank.
Now that the bank thing is settled, lets presume you have a 4 cylinder. As said before, vacuum leaks are a common cause and should be checked early on. There are many ways to do this, but the cheapest and easiest is open the hood and listen for the air whistling/sucking sound and follow it. Doesnt always work, but you may get lucky.

You have a vacuum leak. Did you use new intake manifold gaskets and torque the bolts according to the spec? Did you get all of the vacuum lines back on in the right places?