Nissan Repair: 2001 Pathfinder Acceleration Loss/Sputter, fuel mixture, oxygen sensor

Question
QUESTION: I am experiencing a loss of acceleration primarily when I am traveling at freeways speeds between 50 - 70 mph.  This condition usually, but not exclusively, occurs when I am going up a slight grade or a hill.   When I try to accelerate the car hesitates/sputters and will not maintain speed. It is as if the accelerator disengages. I am lucky if I am able to travel at 50 mph on even a slight grade. During regular city driving the car runs good. At times this also occurs when I go on a freeway on-ramp and as I accelerate and approach about 50 mph.  I have replaced the fuel filter but it has not corrected the problem. The engine service light comes on intermittently. What do you think could cause this problem? Thank you.

ANSWER: Joe,

I would check the fuel pressure to make sure the pump is giving sufficient fuel to feed the car when it is at higher speeds.  Second, go to Autozone or Checker and have the code checked.  Email me back with what you find and we'll go from there.

---------- FOLLOW-UP ----------

QUESTION: Thanks for your reply.  I do not know how to check the fuel pressure on the fuel pump nor do I have access to a fuel pump tester.  I did check the codes and this is what came up:
P0732 - Gear 2 ratio incorrect
P0733- Gear 3 ratio incorrect
P0140- O2 sensor ckt no activity (Bank 1 Sensor 2) the Nissan  code states, Rear O2 Bank 1 high voltage

Thanks again,

Answer
Joe,

The oxygen sensor should be replaced as it could be causing the problems with the shifting.  Since the computer is freaking out over the fuel mixture the vacuum could be off and the computer is shifting the transmission at the wrong time.  Replace the oxygen sensor and disconnect the battery.  Reconnect and see if the codes all stay off.  If not you are looking at the transmission computer is going out or the solenoids on the gears indicated are on their way out.