I installed an adjustable boost contol valve and a calibrated boost gauge last year and have been running at 13.5 psi very successfully until a couple of months ago. Problem occurs when accelerating hard at low speed such as when pulling away from a stop. The boost builds to about 11 psi, but then stops and the engine sputters. If I back off the throttle and try again, it might build past 11psi. No black smoke from the rear when this happens. I did not have any other driveability problems. I turned the boost down incrementally until it maxes at 11psi and the hesitation is gone. I installed a new fuel pressure regulator about a year ago. Any ideas? Fuel pump? Overboost switch? Pressure leak somewhere?

Thanks
Mark