Power loss after extended down shifting is a evap issue. If you still have the evap system in place look for a vacuum leak or a disconnected purge solenoid. If you dont have a power commander, dont eliminate the o2 sensors. You can test this but mileage will suffer, the power commander programming fixes the mileage issue and tunes the performance issues some have found. This will sound stupid but a faulty map sensor or a vaccumm leak on the map sensor lines can also do this.