Imo i dont think a egr would affect boost performance since its only function is to recirculate exhaust gas into the intake to help "cool" the cylinders down. However easy fix would be just remove and plug the vacuum hose going to it. My opinion if you are being restricted on boost check your setup check the hoses and vacuum lines going to the gauge and such. Also how much are you pushing injector wise and what is the setup you run?
1996 Mustang GT, 17x9 front and 17x10.5 cobra r replica rims, 255/40/17 front 285/40/17 rear at the moment,
o/r x-pipe flow master 40 series dump downs, cai/ram intake, 75mm c&l throttle body and plenum, pi heads and intake swap, msd wires, stock gears, untuned at the moment, no dyno numbers for now.