Okay heres the deal. I have been noticing these weird really hard shifts when I was cruising along the interstate, but they were happening so randomly that I wasn't really concerned. But recently its gotten worse and I've narrowed down the problem.

When I'm cruising in 4th gear (in D) and I press the pedal down a little to go a little faster, the RPMs will stay kinda constant instead of increasing, then as I keep pressing the pedal down (Because nothing is happening) it will start shaking. It feels like it doesn't want to downshift from 4 to 3.

Heres where its weird, if I give it more gas right when I want to go faster, instead of just a little like before, it never has problems, it downshifts fine and smooth just like it should.

Then today it came to me that I haven't really floored it in a long time, so I tried that and it seemed to bog down at 4000 RPMs, but I am not 100% sure cuz I really didn't have enough space to test.

I don't know if this is an engine problem or tranny? Any ideas welcome.

 

Well, there's been a couple of problems to plague the monte in those years. I've done some research on this and other sites and I find that MSN is reporting that many users have reported a problem witha transmission sensor that gives false codes of transmission slippage. When the ECM sees transmission slippage it will boost the line pressure in the trans automatically, causing harder shifts. I had problems similar to this prior to trading my 2003 LS. This problem can be remedied with a cheap 10$ sensor and less than an hour of labor at a competent mechanic.

The second problem which can seem to effect the transmission is actually a problem with the Emissions equipment on the Monte Carlo. The stock cat (that is catalytic converter) can become blocked, leading to excess pressure in the exhaust manifold, which will make the car exhibit problems that seem to stem from the transmission. GM, in response to the problem extended the warranty coverage of the exhaustsystem in many models, meaning that even though your bumper-to-bumper coverage (typically 3 year 36k miles) will have expired by now, the problem may be valid for fixing under that warranty. Search other posts for more information. The problem with this solution, however, is that it's not very straightforward to diagnose the manifold backpressure, and if this doesn't happen to be the problem, you have to pay for the diagnosis.

 

Thanks for the info. As for the cat getting clogged though...been there done that. It got clogged a few months ago and thankfully it was still under warranty (at 66,000 miles)

 

Has your mileage gotten much worse as of recent? I'm talking like a 6 MPG drop highway.