I have same issue with my 98 2.5 ATX. Slow at first but then it moves quickly after the car gets to 50 MPH. However there are times when it is cold (i.e. engine not fully warmed up) when it runs well and this symptom is not displayed. Then the nice stataco exhaust note is heard and power is delivered to wheels and acceleration is normal.
Plug changes, UIM/LIM cleaning, IAC valve cleaning, new wires, MAF cleaning all make no difference. TPS is working fine.
It was fine before I had the ATX rebuilt so I suspect it has something to do with that. When starting off from lights after fully warmed up the engine increases revs but no power. Perhaps the IMRC is opening up secondaries too soon. I may try and disconnect to see what happens to acceleration.
