I seem to be one of the few owners of the infamous Dodge 2.7L V6 engine that is relatively happy with it. It is in a 2004 Dodge Stratus SE (VIN 1B3EL36R64N243813) that I purchased new off the dealer lot. It presently has 205k miles on it and I have done most of the maintenance & repairs myself. I changed the oil every 5,000 miles using Mobile 1 full synthetic and a high-quality oil filter every time. I noticed the water pump leaking externally (luckily) in 2016 and I paid to have the timing chain, gear set, tensioner, water pump & oil pump changed. New spark plugs, PCV, air filter and fuel pump / filter were also installed. Also replaced rusty & leaky steel coolant lines at the time of the timing chain work. The engine has always performed well and run strong even with 205k miles on it. Amazingly, the transmission is original and still working well.

A few months after the work described above, the engine suddenly lost power while traveling at 75 MPH on I-75. My daughter was driving and was able to get safely off the expressway and park it. I picked it up with my tow dolly and since that day I have taken it to three (3) mechanics (Dodge Dealer Last) and have spent nearly $1,000.00 with no diagnosis for the problem. The engine runs fine until about 2500 RPM then it sputters, surges and generally malfunctions until the RPM drops below 2500 RPM and runs smooth again. I am amazed how quiet and smooth the engine runs at idle and below 2500 RPM with no clicks, rattles or misses.

The Dodge Dealership initially diagnosed (more of a guess) that the PCM, Crank Sensor & Cam Sensor were bad. They had no codes or real evidence that any these part were bad and admitted as much when I asked if the $1,800.00 they quoted would be guaranteed to fix the problem. They said no guarantee so I let them install new cam & crank sensors. Still, the engine problem at 2500 RPM. After that the Dodge Dealer said they think the PCM is OK and that the problem is and internal engine issue and they would have to tear the engine apart to diagnose it. I declined.

I have had Great Success in maintaining my Jeep Liberty CRD for eleven (11) years with lots of help from forums such as this. I HOPE someone out there has a solution to this problem to share.

 

I had a similar problem with my 06 Strat with the 2.7L. Mine was clogged cats, to which it never threw a code. I had custom headers built and eliminated them all together as it was cheaper than installing new cats.

 

I have not tested the Catalytic Converter myself, but the Chrysler Dealer said it was OK, not that I should necessarily trust them.

I have had catalytic converters fail in two (2) vehicles in my 41 years of driving. The most frustrating was in our Mercury Montego which had dual catalytic converters. The engine ran great sometimes and terribly other times. There was never a specific RPM limit.

The main reason I do not suspect the Catalytic Converter is that the engine runs great below 2500 RPM in park, neutral, or under heavy acceleration. Under all conditions it misses badly & the engine surges at 2500 RPM. Every time that happens, I let off the gas to get the RPM lower then it runs great again.

I have read that the PCM switches from the crank sensor to the cam sensor at about 2500 RPM. The Chrysler Dealer installed new cam and crank sensors but the problem remains.

 

Only reason I say Cat is because your car is doing the same thing my 06 was doing when the front Cat was plugged. The car had 60k on it when this happened.
I ended up getting custom headers, full exhaust, and a tune on it. This cost me about $800, which was about $400 cheaper than replacing the Cats, and being a non-emission state, it didn't matter.