I'm looking for help solving a P101 trouble code on a 2004 Chevy Silverado 2500 with a 6.0L

This truck is new to me, has 150k miles on it and looks to have been through a lot before I got it. I suspect the motor may have been swapped as well.

The engine does seem to lack power beyond 1/2 throttle, 1/2 and 3/4 seem the same and same with full throttle.

It keeps throwing P101 Mass air codes. As soon as you clear it and start to drive the truck, it throws the code.

The engine light in the cluster doesnt work, havent verified if it has been tampered with yet.

So far the following things have been checked/replaced

MAF was replaced twice
Fuel pressure is 62psi
Exhaust pressure is 1.5psi at idle (plugged cats dont seem to be a issue)
Mass air readings seem to be normal using diagnostic tool at service shop (IMO the sensor is reporting correct numbers to ECU right??)
TBW throttle body has been "recalibrated"
ECU has been "flashed & updated" by a service shop (non GM)

Any ideas?? Cant get it to stop throwing the code.

 

I'd suggest check the intregrity of the air intake, this should be free of any (other than filter) obstructions, but more importantly free of any external intake air leaking into it.

 

I have already checked that. Clamps all tight, air filter new/clean, tried running without it once, same results.

 

I found out what was wrong with my truck and wanted to stop back in and update this thread.

Turns out someone had removed the 6.0L motor and put in a 5.3L. Thats why the Mass Air wasnt reading properly, the motor was smaller and pulling in less air than the computer wanted to see.

I had a 6.0L put back in it and now it runs perfect! The trans also shifts much smoother. Truck is perfect again.