2011 Silverado 2500hd setting lean code

[awbrown]

I bought this struck from an auction and other than this one issue It runs and drives like new ... It sets a code saying the engine is lean ..I have had the shop next to mine (I have a machine shop , he is a repair shop ) look at it a few times and it still sets the code ... I can feel a miss or hitch in the engine as I roll into the throttle to increase speed .. It runs fine cruising and if I am hard on the gas .. Anyone had this issue , or have experience with this problem?
Thanks in advance .....