I have a pretty high mileage (217,600 miles) 2000 Monte Carlo LS and a few days ago after I'd gone about 5-10 miles, the car would shift into 4th gear a little earlier than normal. About 2-3 seconds after shifting to 4th, it would drop back to 3rd and then shift back to 4th again. I stopped at a stop light and went to accelerate again and it did the same thing around 4th gear again. Is this a sign of needing transmission work done or is it something as simple as a sensor going out? There isn't a CEL on or any service vehicle/transmission light or anything on. I know if there needs to be transmission work done it's probably not worth the money, but I just dumped about $700 in parts into the suspension and don't want to part with the car.

 

Is it actually shifting to 4th, or is it just the torque converter locking and unlocking.

Could be something as simple as the sensor for that needing to be replaced, or it could be signs of hard part failure.

Check out this link: TCC rpm oscillation

 

could also be the TPS throttle position sensor. remove it and check for smooth operation. and proper spring return. if its all loose and wiggly its bad. faulty TPS can cause that also. 200-250k usually when they go bad on chevy engines.

 

My 04 Monte is "Harsh-shifting"
I have had the infamous PO1811 Shift Adapt Code for many moons.
I've popped for the Jiffy-Lube tranny-douche-job a couple times.

I haven't had to make "The Decision" about what to do when Tranny-time gets here.
I'm leaning toward getting a 100% Re-man with aftermarket Springs and Solenoids the Manager at a nearby AAMCO Shop has recommended.

Advice from those who've been there would be appreciated.

RickCoMatic

 

More than likely the epc solenoid is bad. Is a very common problem on gm cars. Need to drop the drivers side cradle and trans side cover to replace

 

OP, it could be the brake switch also. Do some research on 'torque converter hunting.' Is your issue similar to that? This link might help.

http://www.tripleedgeperformance.com...cillation.html

For what it's worth, mine still kicks out of 4th gear if I don't have progressive acceleration, even after all solenoids, fluid and filter, brake switch, and another torque converter. My car's swapped though, so results may vary.

RickCoMatic, when it's shifting hard/banging into gear erratically, it could very well just be the sensor - as haha chad mentioned. I had the same issue, but replaced all solenoids instead of just the PCS. Last time I drove it, it still shifted quite well, for a 4t65.