My Pathfinder runs fine until it gets to about 30 MPH, then the engines starts running rough. The computer code says the problem is the catalytic converter. The car has about 76k miles. That seems to few miles to have to replace the catalytic converter. Any other suggestions?

Check engine light on? Could be catalytic converters. No engine light. Have history codes read.

check the alternator... battery isn't getting sufficient power from it. if tthe problem continues there will be chance of battery dead. duo to the less power supply from alternator, if we increase the rpm though the vehicle wont go faster and engine gets off. so my suggestion is please check the altrnator replace it if required.

P0340 code means "Something" is wrong in the timing...
from CMP (Camshaft Position sensor) to the crankshaft bolt.

Very first thing, verify connectors are clean and shiny.
clear all codes, even hard codes.

could be catalytic con. plug up.

Try taking the positive battery cable loose for 2 or 3 minutes, this will allow the computer to reset. You probably will still have a check engine light but should run until you can turn it off.

I also have a 2005 pathfinder. I just, today, got p1757 and p1759. I am having the same problem you described. I also noticed the tempature difference. I live miami, fl. I read something about front brake valve solenoid forcing the transmission into a safe mode so there is no pick up. What did you find if anything? Any solutions? Any advice?

check your catalytic converter could be clogged almost positive it is half clogged anyway.inspect the front side.

Change your oxygen sensors - they're responsible for feedback that the computer uses to determine the air/fuel mixture. They usually are good for about 60k miles and then start to go downhill. When they get to a point that the computer won't trust them, it ignores them and runs on preprogrammed fuel maps that run excessively rich (too much fuel) to safeguard the engine. You've probably seen a decrease in fuel mileage as well. And the O2 sensors have to be up around 900 degrees before they'll work - the car ignores them until then. That's why you run fine after a cold start but run rough once the car is warmed up.

The O2 sensors you want to change are in the exhaust system between the engine and catalytic converters (the "pre-cat" sensors). There are O2 sensors after the cats as well, but those are used comparatively to determine how well the cats are functioning. The primaries are the ones used for fuel mixture. If it's been this way for a few weeks or so, I'd put new spark plugs in as well - rich fuel conditions can foul them and contribute to the rough running.

Have you checked your alternator?

bro, check ur main relay. its under the dash. replace it, check also ur distributor(replace it). and also your ECU