06 Monte Shift Hard After Highway
 

Hi all! I have searched this area a few times for advice but finally joined because I am having an issue that I can't figure out!!

I have a 2006 Monte Carlo LT 3.5 with 188,000 and have had a few recent issues that the local mechanic hasn't been able to solve.

Issue 1: I commute about 80 miles to work, 76 of which is straight highway - 80 MPH the whole way. When I first hop in the Monte, start her up, and hit the road...no issues. After I get to either work in the AM or home in the PM, the last few miles, which is city stop and go, is rough. My transmission shifts really hard during those last few miles each way. The kicker...if I park at either work or home, turn it off, and leave it for a few minutes, I can go right back out, start her up, and drive her like she is stolen through town with no hard shifting. But once I repeat the commute or a moderate highway drive, she shifts hard again.

Issue 2: During the above mentioned commute, I have noticed some RPM fluttering. Just cruising along and watching my tach flutter between 2000 and 2200 at about 80 MPH. It isn't a hard surge between that span but enough to where I notice my head bobbing slightly as it is occurring. This is a pretty constant situation as this will continue for the majority of my drive when the cruise is set. However, it does it when the cruise is not set as well.

Both of these issues seemed to start around the same time about 2 or 3 months ago. The engine light did not come on immediately but has started to in recent weeks. The local mechanic flushed the transmission, dropped the pan, and changed the fluid and filter along with adding an additive that they recommended. They also changed the cam sensor and the oil pressure sending unit as they were both throwing codes. This did nothing to help either problem.

Has anyone heard of either of these issues? I am hoping that someone can help as I truly love this car and really don't want to get rid of her but I have to have something to get me from point a to point b and back again each day! She had been an amazing car and super reliable until this recent issue. Thanks in advance everyone!!!

I had the same problem as your Issue#1 I also tried flushing the transmission and it did nothing... the only thing that helped was just like you said shutting the car off for a while and letting the transmission cool down. I also would limit shifting to 3rd gear and not use overdrive when I knew I wasn't going over 50mph. This just limited the number of shifts which seemed to help. The difference was mine happened whether I did highway driving or city. My solution was to either rebuild the transmission or get a certified rebuilt. I think the rebuild was going to cost me $1500 and the certified rebuilt replacement with a 3 yr warranty was close to $5000 installed. I decided to trade it in instead and upgrade to an 07. I hope your fix will be easier than mine and someone on here gives you some more ideas/advise soon!

Quick Update...
 

So I decided to see just exactly how long I have to wait after I shut off my car before I can expect it to shift normally again. I pulled over into a parking lot once I realized that she was shifting hard again after a long trip...I turned off the ignition, waited 30 seconds, started her back up and she shifted perfectly for the last mile home! Turning it off must reset something that temporarily takes care of the problem! I just have no idea what is causing it in the first place!

My 06' Monte was starting to slip actually around 95,000 miles. Not really the same as your problem, but I used the Slick 50 Transmission treatment and it helped tremendously. No more slipping, etc. I don't know, thought I'd throw that out there for you.

https://www.slick50store.com/product...sion-treatment

I have similar issues..
 

this is weird... I had exactly the same problem with my last Monte 2004 3.5 most of the time I owned it. I actually had both the speedo problem and transmission problem. I paid $500 for a dealer to switch out my instrument cluster at the time. Its actually not that hard to do and if it was today I would have done it myself. The guy did it in like 15 minutes. The transmission I did a flush that made it worse actually... not sure if you will have the same result. I would say MAF sensor has nothing to do with your transmission but has to do with your engine. I could be wrong but I don't see how that would have anything to do with it. I never did fix my transmission as the cost to replace it was half as much as a newer monte so I opted to upgrade. I would go to a transmission specialist someone who comes recommended. For $2,500 you could have your transmission completely rebuilt and your instrument cluster replaced. Not sure where they got $3,500 that sounds high.