My friends 2nd gen Problem, NEED HELP

Ok my friend and i were rolling down the highway at about 2500 RPM this past weekend, and all the sudden his 2nd gen eclipse GST went lean on his A/F gauge and his EGT droped from like 12.5 to 6. The car was spitting and sputtering, it only does this if the RPM's stay constant, but the have to be at 2500 or higher. any comments.

He has a 1st gen block (bored 30 over) , 2nd gen head (stock), 2nd gen intake manifold and T-body ( stock), 1st gen cam position sensor ( wired up usingthe magnus motorsports wireing diagram, and the spark plug swap give on magnus motor sports website.), 3" down pipe, greddy evo catback, te turbo is a T4 with a 58 intake and either a 76 or 78 exhaust, he has a D'Jon tools FMIC 32"W 12"H 2.5" Thick, stock ECU, stock injectors, 255 Lph Pump, aftermarket Fuel Regulator.this is what i can think of at the moment if you need to know more ask. Oh yeah it's out of time a bit.

what kind of fuel control is he running?

actually he is running stock ecu and stock injectors, he has a set of 660 and an afc but they have not been installed yet. The problem does not occure when he is underboost situation, but under non-boost conditions.

install the injectors and AFC...