My Mirage sp-sp-sputters

My 95 Mitsubishi Mirage sputters, but only while trying to accelerate. I changed the distributor over a month ago and it ran fine for about 4 weeks. Last week it started sputtering whenever any load is put on the motor, but it will idle and cruise smoothly. I’ve checked the timing (spot on) and changed the TPS, fuel filter, and oxygen sensor. I’ve also checked the fuel pressure and it runs 42 psi, but goes up to 50 when the vacuum line is removed from the fuel pressure regulator. It stays at 42 if the accelerator is increased slowly but will go up to 50 if the accelerator is pressed quickly, as soon as it starts sputtering.
Any ideas at all?