Agree that almost assuredly this is a pegged MAF - assuming you have enough fuel pump. If the top fuel rows are set to a .8 lamda (for instance), even if the load exceeds the load for the top row, the PCM will still command the lamba in the top row provided it's able properly calculate load (ie, maf not pegged). Can't blame this on the tune, not really, unless the tuner knew up front you planned to go that high on boost, and actually was able to log it at that level to get the A/F right. You try not to go too high on load in the fuel and spark tables, unless you know it's going to be used, because you end up losing resolution (there's a limited number of rows to work with) even though the PCM does scale between rows. Unless the tuner wasn't worth his salt, I can't see him not populating the table because he's going to need to rescale them since it only goes to .9 load in the stock tune.

 

I only paid attention to the 2nd paragraph in your first post didn't see the 18 lbs part. My bad.

Now, has anything changed concerning placement of the maf, intake tube, etc? Ultimately it's load we (actually the tune) is concerned with - and the compression ratio of the engine has changed as well as the intake, so think in terms of load instead of boost. At one atmosphere, the new setup flowing 5% more air compared to the new engine - based on calculated the volume at TDC at 8.7:1 compared to 9:1 - and that's assuming all things are equal which they aren't - you've got a new intake manifold as well. So volumetric efficiency has changed. When it clips the A/F ratio is the change sudden and then gets leaner as load increases, or does is it stay steady?