[btwilson86]

Okay, I'm starting to suspect the BOV.

Stock turbo supras came with a bypass valve instead of a blow off valve. Biggest difference between the two is that the bypass valve will redirect excess boost pressure back into the intake pipe between the AFM and the turbo, meaning all of the air stays in the intake system and is accounted for by the AFM. Blow off valves vent the excess pressure to atmosphere. Our computers are programmed to "expect" that air to stay in the intake system, so if it is vented to atmosphere the engine will briefly run rich after shifting (which can cause it to chug and die) because it anticipates more air in the intake than what is actually there.

Basically, as far as the computer is concerned, each time you shift your BOV creates a giant boost leak. The only reason I can think it does it in the higher gears is because it takes longer for the RPMs to get there, allowing you to build more boost pressure thus loose more air/pressure when you shift.