engine dies after warm up

[slicpartna]

I swapped in a 5.3 in my obs

After the engine begins to warm up it cuts off
I dont have the exhaust hooked up yet still with open headers

I get a code for both oxygens sensors (lean conditon)

Is it cutting off because the o2 sensors cant get a good read of the exhuast stream or I have another issue?

[TXsilverado]

get the front 02 sensors installed. sounds like the motor is going into closed loop and the 02 sensors are telling the engine to throw fuel at it until it dies rich.

[slicpartna]

get the front 02 sensors installed. sounds like the motor is going into closed loop and the 02 sensors are telling the engine to throw fuel at it until it dies rich.

The 02 sensors are installed, the rears have been deleted

[farmtruc]

The truck won't run right with open headers