If the car drives well at cruise speed, but lacks power while accelerating, there may be a problem with the fuel pump.Google+
Car Problem Reports
Infiniti Q45 Lack of power on acceleration due to fuel pump issue
Infiniti Q45 Problem
Average Mileage: 159,166 mi (135,000 mi - 180,000 mi)
Visitor, 1995 Infiniti Q45, 162,500 mi
...not fixed yet, but experiencing identical symptoms. Getting some 'backfiring,' (twice recently) also, on accelerating. And, once while starting low gear car came to a near-stop; I pulled over, waited 3 seconds, took off again and no problem.
Visitor, 1992 Infiniti Q45
My car one time decelerating. And shut down with the steering wheel locking up
Visitor, 1995 Infiniti Q45
My 1995 Q45 would not shift into passing excelleration. I changed the fuel pump modual that did not fix it. Then I change the fuel pump and that solved the problem of excelleration.