Mitsubishi Pajero revving and slight loss of power

this problem not always in her - goes out as quick as it comes in! always happens at 70 - 90 km speed and when i accelerate to 100km/hr, it goes out of her. Starts of with this reving noise (not steadying) and then goes bit sluggish - is back at garage for the 3rd time - last time on computer, it put up that injectors had to be reset - done, and was fine for 2 weeks. Back on computer yest, and no faults coming up at all! Any solutions please?????? Driving perfect otherwise.